PHP 5.2 -> 5.3 anomolies

After installing a new ubuntu dev server with 5.3, certain AJAX -> actions did not work anymore.

Digging the code for 2 hours caused grey hairs but solved nothing. Reverting the standard php.ini from 5.3 to our 5.2 did solve the issue. We still need to Diff what exactly caused the problem... Somehow php 5.3 standard returns a Location header that redirects the browser instead of showing the AJAX output... no clue why...