Comment 2 for bug 730495

This isn't actually specific to the guest session. I also get this when running another "real user" session. .xsession-errors complains that unity-window-decorator fails to start because it cannot open display :0.0. This is not surprising, as :0.0 is my primary X session of my own user, and the current X $DISPLAY is :1 or :2. When I start unity-window-decorator in a terminal, it works just fine, though.

Didier, could that be related to the startup checks which session to use? Does anything hardcode display :0 there? I can't see anything obvious in 01_unity_window_decorator.patch, but this issue reproduces perfectly well for me as well.