Can you test with Ubuntu 15.04? Just to know if this is problem in newer versions too.
What do you mean with all processes still running? From .xsession-errors files looks like programs are closed:
App gnome-panel.desktop exited successfully
App unity-settings-daemon.desktop exited successfully
App metacity.desktop exited successfully
...
Maybe problem is somewhere else? Can you post screenshot / image with that purple screen? What should happen when logging out?
Can you test with Ubuntu 15.04? Just to know if this is problem in newer versions too.
What do you mean with all processes still running? From .xsession-errors files looks like programs are closed: daemon. desktop exited successfully
App gnome-panel.desktop exited successfully
App unity-settings-
App metacity.desktop exited successfully
...
Maybe problem is somewhere else? Can you post screenshot / image with that purple screen? What should happen when logging out?