Description:
------------
I expected the last day of given timestamp, but when mktime is the second argument of strtotime this do not happens. So, I need save mktime's result in a variable to use it later in strtotime

Reproduce code:
---------------
<?php
// FAIL !
	$timestamp = time();

	for ($i = 0; $i<10; $i++) {
		$timestamp = strtotime('yesterday', mktime(0,0,0, (date('n', $timestamp) + 1), 1, date('Y')));
		
		var_dump(date('d/m/Y', $timestamp));
	}
?>

<?php
// It's works !
	$timestamp = time();

	for ($i = 0; $i<10; $i++) {
		$timestamp = mktime(0,0,0, (date('n', $timestamp) + 1), 1, date('Y'));
		
		var_dump(date('d/m/Y', strtotime('yesterday', $timestamp))); // here, we have a $timestamp
	}
?>

Expected result:
----------------
string '30/06/2009' (length=10)
string '31/07/2009' (length=10)
string '31/08/2009' (length=10)
string '30/09/2009' (length=10)
string '31/10/2009' (length=10)
string '30/11/2009' (length=10)
string '31/12/2009' (length=10)
string '31/01/2009' (length=10)
string '28/02/2009' (length=10)
string '31/03/2009' (length=10)

Actual result:
--------------
Output of first Code:

string '30/06/2009' (length=10)
string '30/06/2009' (length=10)
string '30/06/2009' (length=10)
string '30/06/2009' (length=10)
string '30/06/2009' (length=10)
string '30/06/2009' (length=10)
string '30/06/2009' (length=10)
string '30/06/2009' (length=10)
string '30/06/2009' (length=10)
string '30/06/2009' (length=10)


Output of second code:

string '30/06/2009' (length=10)
string '31/07/2009' (length=10)
string '31/08/2009' (length=10)
string '30/09/2009' (length=10)
string '31/10/2009' (length=10)
string '30/11/2009' (length=10)
string '31/12/2009' (length=10)
string '31/01/2009' (length=10)
string '28/02/2009' (length=10)
string '31/03/2009' (length=10)