The mitkRenderingManager provides the two methods:
-ForceImmediateUpdate() <- for updating a single render window
-ForceImmediateUpdateAll() <- for updating all render windows

To ensure clean code the ForceImmediateUpdateAll() should call the ForceImmediateUpdate() method for each render window, instead of performing it's own update.

This bug seems to be very easy, but we have to investigate the site effects carefully! Also performance is very important here!