Comment 69 for bug 729979

with a little more digging I think it is this mate_bg_crossfade_start (in ubuntu the same function is gnome_bg_crossfade_start ) IS THE CULPRIT. There was a variable name change from "fading_pixmap" to "fading_surface" and i guess this did not propagate to some compiz related code. For someone in the know, looks like it should be an easy fix.