Description:
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---
From manual page: http://www.php.net/function.strtotime
---

 strtotime('-1 month') has an unexpected behavior in 31th day of month

Test script:
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$t =strtotime('31-07-2017');
echo "\n". date('d/m/Y',$t );
$timestamp = strtotime('-1 month',$t );
echo "\n".date("d/m/Y", $timestamp);
$timestamp = strtotime('-2 month',$t );
echo "\n". date("d/m/Y", $timestamp);
$timestamp = strtotime('-3 month',$t );
echo "\n". date("d/m/Y", $timestamp);
$timestamp = strtotime('-4 month',$t );
echo "\n". date("d/m/Y", $timestamp);
$timestamp = strtotime('-5 month',$t );
echo "\n". date("d/m/Y", $timestamp);




Expected result:
----------------
31/07/2017
30/06/2017
31/05/2017
30/04/2017
31/03/2017
28/02/2017

or 

31/07/2017
01/07/2017
01/06/2017
02/05/2017
02/04/2017
03/03/2017

Actual result:
--------------
31/07/2017
01/07/2017
31/05/2017
01/05/2017
31/03/2017
03/03/2017