Checkout the integration branch and test the new 2D VTK rendering.
Very important:
-try if you own rendering stuff (e.g. QBalls and other rendering extensions) are still working.
-this bug is only about 2D rendering!!! So don't worry about the 3D render window and compare the 2D render windows to an older version of MITK (e.g. 3M3).
Attached you can find some nice test images.