http://bugs.php.net/bug.php?id=46889 PHP bug list obviously. While it may be the user's problem, it would be a good idea of advising the users either in a readme file of some sort of a known issue with a known version. That way they're not blaming you for crashes calling your script crap because of a bug out of your control.
Yes, I know it's from the buglist. But you just showed me bug #46889. Do you know every single memory leak in every single version of PHP? Probably impossible.