How to correctly navigate between BSP controllers?

We have a BSP application called in the browser via the main controller "main.do". Via a link the user can navigate to another controller "usereinstellungen.do" like this:

<htmlb:link id = "settings"

text = "Settings"
tooltip = "Change User Settings"
reference = "usereinstellungen.do" />

This works fine, the new controller's view is loaded in the browser. I noticed however that the browser's address bar still shows the address with "main.do", so apparently the other controller (view) is loaded in a frame.

Now to my problem. In the view of the second controller there is a link again that should jump back to the main application, i.e. from "usereinstellungen.do" back to "main.do". However, as soon as the user clicks on that link the browser just shows an empty white page. Nothing else happens.

I checked in ST22, but no dump. I also set a breakpoint in the INIT and REQUEST methods of the main controller ("main.do"), but these don't fire. Those breakpoints do fire however when I force to reload the page via F5 key in the browser.

Any ideas what could be the problem here?