After installing libX11-1.5.99.902 and libXau-1.0.8 I see strange effects on
systems with NVidia cards.
At the first system (Gallium 04 on NV86 - NVIDIA Corporation G86M [Quadro NVS
140M]) the gnome desktop background is set to a green gradient, but only a
black background is shown.
At the second system, gnome systems settings says Gallium 0.4 on NVD9 - Forced
Fallback modus On (NVIDIA Corporation GF119 [GeForce GT 520]) the the desktop
background is not refreshed. If I switch at the second system to the 3D mode,
the issue with the background disappears but the desktop is frequently
crashing.

This bug is also filed as a gentoo bug at 

https://bugs.gentoo.org/show_bug.cgi?id=471396.