With a Radeon HD 7770 on the radeonsi, when I resize windows to a smaller size, they flash and become black... then you have to resize them up a bit for their contents to be visible again. I also get a bug where parts of large GTK3 windows will become black when there are more than a few windows running on the desktop. Pitivi 0.91 is particularly good at triggering this when maximized at 1920x1080. Tried with the 3.9 kernel, 3.10, 3.11 with DPM activated... no luck.
Created attachment 808813 [details] lspci -vvvv
Created attachment 808820 [details] dmesg
Created attachment 808821 [details] Xorg log
Woohoo, this bug is gone in F20!