Comment 17 for bug 302227

I am not sure if this will still be seen by the upstream developers, but I think I have a better way of describing the problem that suggests it has a very simple fix.

Since the redraw vestiges happen only outside an 800x600 window (the same size the greeter used), it is possible that the background window (or however it may be called in Z/Compiz-speak) responsible for ensuring things get erased when needed is being sized at the same size the greeter used (800x600 in this case) instead of the size of the combined monitor area (2048x768).

I hope this helps.