I had a 15.04 system where the window manager decorations disappeared after I installed Nvidia drivers. I removed and purged them, but the decorations never came back.
So I reinstalled to 14.04, hoping this would fix things. With 14.04 and Nouveau, things worked fine, but when I mounted my
/home disk from the old system, the window decorations disappeared again. I tried renaming
.cache/compizconfig-1/, and then
.cache/ but neither did anything. Where is the offending file?