I'm using Debian Buster with PHP 7.3 and xdebug from the distribution.

I noticed the bug in the following code (Stram.php from zend-dactiros):

public function rewind()
{
    return $this->seek(0);
}
public function seek($offset, $whence = SEEK_SET)
{
   ...
   fseek($r, $offset, $whence)
   ...
}

$whence is a default parameter and should be SEEK_SET when not explicitly passed. But sometimes $whence becomes null instead of 0 and fseek fails. With sometimes I mean the first call(s) are OK, but then the error happens.
When I change $this->seek(0) to $this->seek(0, SEEK_SET) there is no error, but other code parts may fail.

This happens even if I'm only enabling xdebug but not debugging at all.

My xdebug.ini is pretty straightforward:
zend_extension=xdebug.so
xdebug.remote_enable=on
xdebug.remote_host=localhost
xdebug.remote_port=9100
xdebug.remote_handler=dbgp