Not responding to touch input after phone call
I've had that twice on byzantium: after ending a phone call the shell does not react to touch input anymore. Clock continues, wifi strenght changes, ... so the shell is still running. stracing shows the compositor also forwards input events. Event system modal dialogs continue to 'work' as in squeekboard folds out an text is input at the right place on just can't click o.k.
A quick look at
proximity.c shows a possible problem but i did not manage to reproduce this yet without calls running over the lock screen.