Hi Alberto,
This is one of those cases where the complexity of the underlying code rears it's head. Remember the server, and browser are "mimicking" a "program" but it's fundamentally doing something the browser was not meant to do.
Answering your question is somewhat complex, so instead I've added a setting for build PR35.
On the form, advanced tab, you can now set the "default form action" and the value of the unique key field if the action is "change".
I'm hoping to upload PR 35 later today.
Cheers
Bruce