Description:
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(sorry for my english i'm french )
using timestamp incrementation with date(H), i found somme datetime error : 
the error occur on the same hours ( 02:00 ) 

echo date("Y/m/d H:i",gmmktime(2,0,0,03,25,2007)) -> 2007/03/25 03:00

reproductible on every years same month ( end mars ) 
2007/03/25 03:00,2008/03/30 03:00,2009/03/29 03:00,2010/03/28 03:00
2011/03/27 03:00,2012/03/25 03:00,2013/03/31 03:00,2014/03/30 03:00
2015/03/29 03:00 ...

to find date errors run the code 

found on windows/wamp 1.5.0 (php 5.1)
tested on linux/mandriva/appache with php 4.1
all plateform test is x86 

Reproduce code:
---------------
<?php
session_cache_expire (0);
echo '<pre>';
  $dt1=mktime(0,0,0,1,1,2007);
  echo date("Y/m/d H:i",$dt1)."\n";
  for ($i=1;$i<24*365*20;$i++){
    set_time_limit(0);
    $dt2=mktime(date("H",$dt1)+1,date("i",$dt1),0,date("m",$dt1),date("d",$dt1),date("Y",$dt1));
    $d=date("H",$dt2)-date("H",$dt1);
    if ($d<>1 and $d <>-23) {
        echo date("Y/m/d H:i",$dt1)." ".date("Y/m/d H:i",$dt2)."\n";
    flush();
    }
    $dt1=$dt2;
  }
  echo date("Y/m/d H:i",$dt2)."\n";
echo '<pre>';
?>


Expected result:
----------------
echo date("Y/m/d H:i",gmmktime(2,0,0,03,25,2007)) -> 2007/03/25 02:00

Actual result:
--------------
echo date("Y/m/d H:i",gmmktime(2,0,0,03,25,2007)) -> 2007/03/25 03:00