This problem only exists in the update transactions.
I also have two insert forms and they DO redirect to another page after submitting.
Too me this seems strange because 'insert' and 'update' use the same "Trigger_Default_Redirect" so the difference seems to be in KT_Insert1 and KT_update1.
I tested my site local with the same PHP version my host uses, PHP 5.2.11 and local the site works like a charm!!! Online I keep having the same trouble. I even just now changed my DB out of enormous frustration I guess... nothing helps...
PS Thanks Günter Schenk for your answer on the blanc page problem but I'm afraid that is not it.
By now I have - like some other users - also installed the "wampserver" (which allows for switching between multiple PHP versions) in order to test the currently available ADDT "PHP 5.3.0 compatible" user-contributed fixes and have to say that some fixes work under certain circumstances, but others don´t and even break more stuff than I anticipated, what´s quite frustrating.
The issue with trying to make ADDT compatible with PHP 5.3 is: it´s a complex framework with lots of PHP files and heaps of function dependencies which may of course be well reproducible to those who developed ADDT in the first place, but not to us regular users who may have successfully managed to modify one single function in the past, but are now struggling with trying to grasp the "whole thing", what´s probably out of reach.
As far as I´m concerned, I fear that I´m currently not able to help with any PHP 5.3.0 related ADDT issues