Description:
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This issue seems to be closely related to bug 36367. While the gmdate function returns correctly, the gmmktime function returns an incorrect timestamp - the "offset" from localtime to GMT being in the wrong direction.

I am running Apache 2.0.59 in South Africa (GMT +0200). If I am 2 hours later than GMT, then the GMT timestamp equivalent to my local time must surely be less by 7200 - not more.

Reproduce code:
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<?php
$time1=mktime(15,0,0,1,15,2006);
$time1a=date("Y-m-d,H:i", mktime(15,0,0,1,15,2006));    
echo $time1a."<br />"; //displays 2006-01-15,15:00 (correct)
$time2=gmmktime(15,0,0,1,15,2006);
$time2a=gmdate("Y-m-d,H:i", mktime(15,0,0,1,15,2006));
echo $time2a."<br />"; //displays 2006-01-15,13:00 (correct)
$hrsdiff=($time1-$time2)/3600;
echo $hrsdiff."<br />";            //displays -2 (incorrect)
echo $time1."<br />";        //displays 1137330000 (correct)
echo $time2."<br />";        //displays 1137337200 (incorrect)
$hr1=date("H",$time1);
$hr2=date("H",$time2);
echo $hr1."<br />";          //displays 15 (correct)
echo $hr2;                   //displays 17 (incorrect)
?>


Expected result:
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If localtime is 2 hours later than GMT, $time2 should be 1137322800; $hrsdiff should be +2; $hr2 should be 13

Actual result:
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As shown in code comments