If you find your Ubuntu frozen after pressing ALT-TAB for the Application Switcher from the Compiz feature, you can follow these steps to fix it:
1. Open Compiz Configuration.
2. Uncheck the Reflection checkbox.
3. And you won’t have a problem with Application Switcher anymore.
I think this is considered a bug in Compiz. Let’s hope that they can fix it in a later release. Thanks for reading and don’t forget to leave any comments.