Description:
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When involving the 31st of October (either by finding out number of days between 2005-10-29 and 2005-10-31 or 2005-10-31 and 2005-11-01), it gives the wrong result.

Days between 2005-10-29 and 2005-10-30 returns 1 (which is correct), however, days between 2005-10-29 and 2005-10-31 returns 3 (which is incorrect, it should be 2).

It seems to work fine for 2001, 2002, 2003 and 2006-2009, not for 2004 and 2005 (as stated above).

Reproduce code:
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$dos = "2005-10-30"; 

$year = substr($dos, 0, 4);   
$month = substr($dos, 5, 2);   
$day = substr($dos, 8, 2);   

$mktime_dos = mktime(0, 0, 0, $month, $day, $year);   

$next_month = "2005-11-01"; 

$year = substr($next_month, 0, 4);   
$month = substr($next_month, 5, 2);   
$day = substr($next_month, 8, 2); 

$mktime_now = mktime(0, 0, 0, $month, $day, $year);   

$difference = $mktime_now - $mktime_dos; 
$signed_up_days_ago = ceil($difference / 60 / 60 / 24); 

echo $signed_up_days_ago . "\n";


Expected result:
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2

Actual result:
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3