This is driving me to drink more than I already do. One laptop. One external screen to the right of the laptop. Desktop extending to the right onto the second screen.
Open a file in QuicktimeX, drag it to the second screen, hit play, hit full screen.
Now, what used to happen, is it went full screen. I have something running on the external screen, while poking around on my main screen.
Instead, when I hit full screen, it goes full screen on the laptop screen, and whatever was on the external screen, kinda slides in behind QuicktimeX, leaving me with a blank external screen.