can no more POST after update 2.3.3

after updating a production rails site from 2.3.2 to 2.3.3 everything
works fine.

But i cannot POST any form without getting public/500.html rendered.

What especially is annoying that i get _NOTHING_ in production.log -
just nothing. How to debug? I get the hit in the webservers log and i
get the public/500.html rendered correctly. But nothing in
production.log.

When i process the same form with method GET everything works 100% Ok.

Please help.

more information: it was not the update to rails-2.3.3 but it seams
the
update of ruby-1.9.1-p129 to ruby-1.9.1-p243 causes the troubles.