Comment 23 for bug 1242115

...And now the problem is gone again. Things I did:
- use the open source intel drivers for X, using software-properties-gtk (done that multiple times before to no avail)
- Install Mir
- complete shutdown because of low battery
- Disable Mir because it doesn't work (by simply removing the lightdm entry)
- Notice that compiz now works as it should, no black areas
- be stumped

There were some updates in between as well but not to xorg or compiz I think.
So my problem is solved, for now. I don't know how.