One thing I noticed with PHP Versions >= 5.2 and Large Content (site BODY containing more than 100.000 Characters) is that MX-Includes can not process them any more because with PHP 5.2 the PCRE Backtrack Limit was implemented.
In this case MX Includes will fail silently without letting you know that anything went wrong - it just won't render the body any more.
This can simply be solved by calling this before the Interakt includes:
ini_set("pcre.backtrack_limit", 1000000); ini_set("pcre.recursion_limit", 1000000);
Hope this will help someone! ;-)