I'm having the same problem here. The following steps reliably reproduce the issue for me:
From the lobby click on a room.
Press Cmd-H to hide the app. (This works).
Click the Dock icon for Propane
Press Cmd-H to hide the app again. (This doesn't work).
At this point no keystrokes appear to work, be that Cmd-H, Cmd-W, Cmd-Q or even letters. Clicking on any interactive control within the window will make keys work again. Based on my limited Cocoa experience I'd guess there was no First Responder.