Alt+Tab = Frozen Frame

[HardCoreShooter]

I've encountered this bug many times. This time I Alt+Tabbed in the Lobby. Then go back to killersource and the game is somewhat frozen but not actually since behind the frozen frame, I can still click buttons or do everything normally. I even quick joined and press randomly on where the start button would be and it joined the game but the frozen frame is still on top of everything.

Current Video Settings:
Everything sets to low except model quality which is set to the highest.
Fullscreen

Steps to reproduce:
Alt+Tabbing for 1 minute+