How to reproduce:
1.boot
2. kdm (xorg/mesa init)
3. systemctl stop kdm 
4. weston // problematic
5. alt-ctrl-bckspace
6. systemctl start kdm
7. desktop (without effects or 3D)
8. logout
9. systemctl stop kdm
10. weston (without described flickering)

Screenshots:
http://212.158.157.7/20130907_001.jpg (weston start - triangle damaged title)
http://212.158.157.7/20130907_002.jpg (first input in terminal)
http://212.158.157.7/20130907_003.jpg (terminal filled)

On every redraw (input from keyboard), all damaged content (triangles) flicker.

Kernel 3.9.1, mesa git, llvm git, weston+wayland git.