I've noticed that when I'm playing Aces High III, if I Alt+Tab to get out of the game for whatever reason, I turn my headset quite a bit (e.g., 60 degrees or more), then (while still looking in the different direction) Alt+Tab back into the game, I have a bad time. It's hard to describe, but basically, after that point in time, if I rotate my head again about that far (e.g., 60 degrees or so) to the side causes the game to "fade out" in VR (so like, I'm looking at the SteamVR loading screen instead, and it says "Waiting for Aces High III..." or similar), and if I turn my head back to where it was before, it causes the game to "fade in" again, and I'm back in my cockpit. This makes the game unplayable until I restart it.
Anyone else get anything like that? I guess the work-around is to just never alt-tab while playing, which is not so great.