I have this problem too in both the latest and the previous beta.
A couple of different ways it happens.
First, I go to full screen using CTRL - F. Works fine. I can exit out using the same command.
However, if I hit the play button to pause it first, it goes into the can't exit without task manager bug.
Same thing if I hit the full screen icon on the bottom right.
There seems to be a few different things that cause it. I know I hit a different key combo once but wasn't paying attention so didn't catch what it was (I'm sometimes a tad clumsy
).