Apps may hang when switching between them.

For example, here is the case, which 100% hangs the drawing.

1) Open YouTube app

2) Start playing a video

3) Open another app

4) It second app hangs.

5) Go back to first app - it is also hanged. 

Most probably, it happens because we don't honor Active, Inactive, Visible, Invisible and other events from libwindowmanager. Going to implement them and see if something happens.