This will be interesting, because top.location will not change if the action is a straight POST. This will be interesting to see how you make out Sva.
As usual I spout useless shit most of the time.
Anyway if u filter the useless shit

Basically u have an iframe with a post form lets say.
You either listen for location of iframe (by polling) to change or maybe u can detect the click on the form button.
Then u do not redirect the "top", you just change the content with JS.
If u redirect the top, then the iframe will reload.