Following function can cause the problem:
<?php

/**

• Log and display the error
• @param string $group Name of error group to report
• @param string $error Error to report
• @param object/array $object Object to include with the log
• @param bool $backtrace TRUE if watchdog log should include full backtrace of the error
  */
  function aat_wex_log($group, $error, $object = NULL, $backtrace = TRUE) {
  $object_msg = $object ? 'Object: ' . var_export($object, TRUE) : '';
  $bt = $backtrace ? 'Backtrace: ' . var_export(debug_backtrace(), TRUE) : '';
  watchdog($group, "Error message: %error
  \n%object
  \n%bt", array('%error' => $error, '%object' => $object_msg, '%bt' => $bt), WATCHDOG_ERROR);
  $last_id = db_query("SELECT 1", array(), array('return' => Database::RETURN_INSERT_ID));
  $msg = t("Error: !id", array('!id' => $last_id));
  $err_msg = user_access('access site reports') ? l($msg, 'admin/reports/event/' . $last_id) : $msg;
  drupal_set_message($err_msg, 'error');
  }
  ?>
  This is the only place, where I'm using var_export().

Usually this function is executed when there is an Exception (try/catch).

This is what was called in PHP before the crash:
24.3217 54977744 -> Database::getConnection($target = ???, $key = ???) /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:2685 => $key = 'default' /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:1444

=> class DatabaseConnection_mysql { protected $shutdownRegistered = FALSE; protected $target = 'default'; protected $key = 'default'; protected $logger = NULL; protected $transactionLayers = array (); protected $driverClasses = array ('InsertQuery' => 'InsertQuery_mysql', 'MergeQuery' => 'MergeQuery', 'DatabaseTransaction' => 'DatabaseTransaction', 'SelectQuery' => 'SelectQuery', 'DeleteQuery' => 'DeleteQuery', 'DatabaseSchema' => 'DatabaseSchema_mysql', 'UpdateQuery' => 'UpdateQuery'); protected $statementClass = 'DatabaseStatementBase'; protected $transactionSupport = TRUE; protected $transactionalDDLSupport = FALSE; protected $temporaryNameIndex = 0; protected $connectionOptions = array ('database' => 'aat_clean_drupal2', 'username' => 'root', 'password' => 'root', 'host' => 'localhost', 'port' => '', 'driver' => 'mysql', 'prefix' => array (...)); protected $schema = class DatabaseSchema_mysql { protected $connection = ...; protected $placeholder = 0; protected $defaultSchema = 'public'; protected $uniqueIdentifier = '4fd0724f48a245.45588987' }; protected $prefixes = array ('default' => ''); protected $prefixSearch = array (0 => '{', 1 => '}'); protected $prefixReplace = array (0 => '', 1 => '') } 24.3219 54977744 -> DatabaseConnection->schema() /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:2685
=> class DatabaseSchema_mysql { protected $connection = class DatabaseConnection_mysql { protected $shutdownRegistered = FALSE; protected $target = 'default'; protected $key = 'default'; protected $logger = NULL; protected $transactionLayers = array (...); protected $driverClasses = array (...); protected $statementClass = 'DatabaseStatementBase'; protected $transactionSupport = TRUE; protected $transactionalDDLSupport = FALSE; protected $temporaryNameIndex = 0; protected $connectionOptions = array (...); protected $schema = ...; protected $prefixes = array (...); protected $prefixSearch = array (...); protected $prefixReplace = array (...) }; protected $placeholder = 0; protected $defaultSchema = 'public'; protected $uniqueIdentifier = '4fd0724f48a245.45588987' }
24.3219 54977744 -> DatabaseSchema->createTable($name = 'ctools_object_cache', $table = array ('description' => 'A special cache used to store objects that are being edited; it serves to save state in an ordinarily stateless environment.', 'fields' => array ('sid' => array (...), 'name' => array (...), 'obj' => array (...), 'updated' => array (...), 'data' => array (...)), 'primary key' => array (0 => 'sid', 1 => 'obj', 2 => 'name'), 'indexes' => array ('updated' => array (...)), 'module' => 'ctools', 'name' => 'ctools_object_cache')) /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:2685 24.3220 54978680 -> DatabaseSchema_mysql->tableExists($table = 'ctools_object_cache') /Users/kenorb/Sites/AAT/docroot/includes/database/schema.inc:656 24.3221 54979240 -> DatabaseConnection_mysql->queryRange($query = 'SELECT 1 FROM {ctools_object_cache}', $from = 0, $count = 1, $args = ???, $options = ???) /Users/kenorb/Sites/AAT/docroot/includes/database/mysql/schema.inc:507 24.3221 54980672 -> DatabaseConnection->query($query = 'SELECT 1 FROM {ctools_object_cache} LIMIT 0, 1', $args = array (), $options = array ()) /Users/kenorb/Sites/AAT/docroot/includes/database/mysql/database.inc:82 24.3221 54982784 -> DatabaseConnection->defaultOptions() /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:651 >=> array ('target' => 'default', 'fetch' => 5, 'return' => 1, 'throw_exception' => TRUE) => $options += array ('target' => 'default', 'fetch' => 5, 'return' => 1, 'throw_exception' => TRUE) /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:651 24.3222 54983960 -> DatabaseConnection->expandArguments($query = 'SELECT 1 FROM {ctools_object_cache} LIMIT 0, 1', $args = array ()) /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:662
=> $modified = FALSE /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:714
24.3223 54985856 -> array_filter(array (), 'is_array') /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:718
=> array ()
=> FALSE 24.3223 54983960 -> DatabaseConnection->prepareQuery($query = 'SELECT 1 FROM {ctools_object_cache} LIMIT 0, 1') /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:663 24.3223 54984312 -> DatabaseConnection->prefixTables($sql = 'SELECT 1 FROM {ctools_object_cache} LIMIT 0, 1') /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:461
24.3224 54984632 -> str_replace(array (0 => '{', 1 => '}'), array (0 => '', 1 => ''), 'SELECT 1 FROM {ctools_object_cache} LIMIT 0, 1') /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:429 >=> 'SELECT 1 FROM ctools_object_cache LIMIT 0, 1' >=> 'SELECT 1 FROM ctools_object_cache LIMIT 0, 1' => $query = 'SELECT 1 FROM ctools_object_cache LIMIT 0, 1' /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:461
24.3224 54984472 -> PDO->prepare('SELECT 1 FROM ctools_object_cache LIMIT 0, 1') /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:464 24.3225 54985776 -> DatabaseStatementBase->__construct($dbh = class DatabaseConnection_mysql { protected $shutdownRegistered = FALSE; protected $target = 'default'; protected $key = 'default'; protected $logger = NULL; protected $transactionLayers = array (); protected $driverClasses = array ('InsertQuery' => 'InsertQuery_mysql', 'MergeQuery' => 'MergeQuery', 'DatabaseTransaction' => 'DatabaseTransaction', 'SelectQuery' => 'SelectQuery', 'DeleteQuery' => 'DeleteQuery', 'DatabaseSchema' => 'DatabaseSchema_mysql', 'UpdateQuery' => 'UpdateQuery'); protected $statementClass = 'DatabaseStatementBase'; protected $transactionSupport = TRUE; protected $transactionalDDLSupport = FALSE; protected $temporaryNameIndex = 0; protected $connectionOptions = array
('database' => 'aat_clean_drupal2', 'username' => 'root', 'password' => 'root', 'host' => 'localhost', 'port' => '', 'driver' => 'mysql', 'prefix' => array (...)); protected $schema = class DatabaseSchema_mysql { protected $connection = ...; protected $placeholder = 0; protected $defaultSchema = 'public'; protected $uniqueIdentifier = '4fd0724f48a245.45588987' }; protected $prefixes = array ('default
' => ''); protected $prefixSearch = array (0 => '{', 1 => '}'); protected $prefixReplace = array (0 => '', 1 => '') }) /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:0
=> $this->dbh = class DatabaseConnection_mysql { protected $shutdownRegistered = FALSE; protected $target = 'default'; protected $key
= 'default'; protected $logger = NULL; protected $transactionLayers = array (); protected $driverClasses = array ('InsertQuery' => 'InsertQuery_mysql', 'MergeQuery' => 'MergeQuery', 'DatabaseTransactio
n' => 'DatabaseTransaction', 'SelectQuery' => 'SelectQuery', 'DeleteQuery' => 'DeleteQuery', 'DatabaseSchema' => 'DatabaseSchema_mysql', 'UpdateQuery' => 'UpdateQuery'); protected $statementClass = 'Dat
abaseStatementBase'; protected $transactionSupport = TRUE; protected $transactionalDDLSupport = FALSE; protected $temporaryNameIndex = 0; protected $connectionOptions = array ('database' => 'aat_clean_d
rupal2', 'username' => 'root', 'password' => 'root', 'host' => 'localhost', 'port' => '', 'driver' => 'mysql', 'prefix' => array (...)); protected $schema = class DatabaseSchema_mysql { protected $conne
ction = ...; protected $placeholder = 0; protected $defaultSchema = 'public'; protected $uniqueIdentifier = '4fd0724f48a245.45588987' }; protected $prefixes = array ('default' => ''); protected $prefixS
earch = array (0 => '{', 1 => '}'); protected $prefixReplace = array (0 => '', 1 => '') } /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:2114
24.3226 54986216 -> PDOStatement->setFetchMode(5) /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:2115

=> TRUE
=> NULL
=> class DatabaseStatementBase { public $dbh = class DatabaseConnection_mysql { protected $shutdownRegistered = FALSE; protected $target = 'default'; protected $key = 'default'; protected $logger = NULL; protected $transactionLayers = array (...); protected $driverClasses = array (...); protected $statementClass = 'DatabaseStatementBase'; protected $transactionSupport = TRUE; protected $transactionalDDLSupport = FALSE; protected $temporaryNameIndex = 0; protected $connectionOptions = array (...); protected $schema = class DatabaseSchema_mysql { ... }; protected $prefixes = array (...); protected $prefixSearch = array (...); protected $prefixReplace = array (...) }; public $queryString = 'SELECT 1 FROM ctools_object_cache LIMIT 0, 1' }
=> class DatabaseStatementBase { public $dbh = class DatabaseConnection_mysql { protected $shutdownRegistered = FALSE; protected $target = 'default'; protected $key = 'default'; protected $logger = NULL; protected $transactionLayers = array (...); protected $driverClasses = array (...); protected $statementClass = 'DatabaseStatementBase'; protected $transactionSupport = TRUE; protected $transactionalDDLSupport = FALSE; protected $temporaryNameIndex = 0; protected $connectionOptions = array (...); protected $schema = class DatabaseSchema_mysql { ... }; protected $prefixes = array (...); protected $prefixSearch = array (...); protected $prefixReplace = array (...) }; public $queryString = 'SELECT 1 FROM ctools_object_cache LIMIT 0, 1' }
=> $stmt = class DatabaseStatementBase { public $dbh = class DatabaseConnection_mysql { protected $shutdownRegistered = FALSE; protected $target = 'default'; protected $key = 'default'; protected $logger = NULL; protected $transactionLayers = array (...); protected $driverClasses = array (...); protected $statementClass = 'DatabaseStatementBase'; protected $transactionSupport = TRUE; protected $transactionalDDLSupport = FALSE; protected $temporaryNameIndex = 0; protected $connectionOptions = array (...); protected $schema = class DatabaseSchema_mysql { ... }; protected $prefixes = array (...); protected $prefixSearch = array (...); protected $prefixReplace = array (...) }; public $queryString = 'SELECT 1 FROM ctools_object_cache LIMIT 0, 1' } /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:663
24.3228 54985160 -> DatabaseStatementBase->execute($args = array (), $options = array ('target' => 'default', 'fetch' => 5, 'return' => 1, 'throw_exception' => TRUE)) /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:664
24.3229 54986792 -> is_string(5) /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:2120
=> FALSE
24.3229 54986792 -> PDOStatement->setFetchMode(5) /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:2127
=> TRUE
24.3229 54986752 -> DatabaseConnection->getLogger() /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:2131
=> NULL
=> $logger = NULL /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:2131
24.3230 54986888 -> PDOStatement->execute(array ()) /Users/kenorb/Sites/AAT/docroot/includes/database/database.inc:2136

Can't reproduce on PHP 5.3.6 with xdebug enabled.

Keborb, it would be really helpful if you could reproduce this with one single small script that doesn't rely on anything Drupal.

Could you please provide the requested information?

No information provided and I can't reproduce this. Closing, but feel free to reopen if you can provide the requested information.