Description:
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I have a script, that got sometimes a date - related error message but nowhere is such a function called. I don't got the errors myself, I see them just in my error log from other users.

Maybe this is not a bug, but i'm searching for a few days for a solution and have no explanation why this bug at line 26 after a flush(); appears (line 26 is marked as a comment in "Actual result:"). The error don't appear at the most time. This is very randomly.

Reproduce code:
---------------
<?php
	header('Expires: Tue, 19 Jan 2038 03:14:07');
	header('Last-Modified: Thu, 01 Jan 1970 00:00:00');
	header('Cache-Control: public');
	require_once($global['path'].'core/global/functions/mime_type.php');
	if(!$mime_type=mime_type($_GET['file']))
		if(isset($_GET['mime_type']) && ($_GET['mime_type']==='image/bmp' || $_GET['mime_type']==='image/gif' || $_GET['mime_type']==='image/jpeg' || $_GET['mime_type']==='image/png' || $_GET['mime_type']==='text/css' || $_GET['mime_type']==='text/html'))
			$mime_type=$_GET['mime_type'];
		else
			$mime_type='text/plain';
	header('Content-type: '.$mime_type.'; charset=utf-8');
	$size=filesize($_GET['file']);
	$file=fopen($_GET['file'],'rb');
	if($global['server_configuration']['compress_'.$mime_type]==='TRUE')
		ob_start('ob_gzhandler');
	else
		ob_start();
	while($size>$global['server_configuration']['output_buffer'])
	{
		$size-=$global['server_configuration']['output_buffer'];
		echo fread($file,$global['server_configuration']['output_buffer']);
		if($size>0)
		{
			ob_flush();
			flush();
		}//This is line 26
	}
	if($size>0)
		echo fread($file,$size);
	ob_end_flush();
	fclose($file);
	exit();
?>

Actual result:
--------------
Warning: main(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'Europe/Paris' for '1.0/no DST' instead in E:\Programme\Lokaler Server\Apache Software Foundation\Apache2.2\htdocs\tower-defense\core\global\includes\load_content.php on line 26


If needed I can post the declared variables at the moment the error appears or other related scripts.