5
You really need to update PHP to at least 5.3.7
There will be soon PHP 5.6.0, and normally we support only the three current versions, which right now is:
5.3.x
5.4.x
5.5.x
I don't even have anywhere PHP 5.2.x to test anything there. All my tests are done on PHP 5.5.10, because it is the strictest version in regard to errors.
I have tested the current version from the trunk on two different installations, and in both cases it worked OK.
Please upgrade to PHP 5.3.7+ or PHP 5.4.x, and to XOOPS 2.5.6 or you can even try to test the 2.5.7 beta version, and see if the problem is still there.