Tim wrote to PHP internals list, asking:
is there any intention to backport this simple but important bugfix to PHP 4? Many PHP users are still using PHP 4, and it's not a very well advertised fact that it does not properly support arrays with more than 64K entries.
Just change to 5.
It seems that MediaWiki HEAD branch will drop php4 support soon.
i do not see any reasons why one should not change to php 5.