Dear Maintainer,

After latest upgrade of libkwineffects there started problems with rendering of
some of desktop effects:
- when desktops are switched with Cube Desktop, there is visible black
rectangle at top right quarter of screen
- when there is used wall of desktops, then window is not visible when is
dragged betwenn destops.
The problems are better described on this video: https://youtu.be/H8LQPbsePiE

I suppose that the problems have something in common because they appeared at
the same time.