Here's my problem.
I a ha form in a "create" controller "index.php/ot/create/"
the init_form points to a "save/" controller.
There's no problem on that, all works fine, but the URL remains "index.php/ot/create/" ... so a refresh (F5) of the page will submit the form again and recreate another invoice ...
I found the quick and dirty way :
but if a better idea is known, I'll take it !