make sure:
xdebug.overload_var_dump = 1
run code:
<?php
error_reporting(E_ALL);
$mysql_host = "ensembldb.ensembl.org";
$mysql_username = "anonymous";
$mysql_password = "";
$mysql_database = "";
$h=new MySQLi($mysql_host,$mysql_username,$mysql_password,$mysql_database);
$res=$h->query('SELECT 1 AS test');
var_dump($res,$res->num_rows);
die();
?>

Expected result:
(warning: sorry, im too lazy to format it to xdebug-style :p)
object(mysqli_result)0000002 (5) { ["current_field"]=> int(0) ["field_count"]=> int(1) ["lengths"]=> NULL ["num_rows"]=> int(1) ["type"]=> int(0) } int(1)

Actual result:

object(mysqli_result)[2]
public 'current_field' => null
public 'field_count' => null
public 'lengths' => null
public 'num_rows' => null
public 'type' => null

int 1