I was recording a game this evening (the Dolphin emulator, to be precise), and was simultaneously exporting a video from Shotcut (the video editor). While playing, I brought up Shotcut on my other monitor to check the progress. I use Chrome on my other monitor all the time, so I didn't think this would be an issue. However, the video capture from Action switched to Shotcut at this point and never switched back (despite the fact that I minimized Shotcut and probably did stuff in Chrome later on).
I was recording in Game mode, which had already selected Dolphin. I did notice earlier that for whatever reason, Action considers Shotcut a "game". But even if hypothetically I started another actual game, Action should not switch games in the middle of recording, imo, any more than it would switch applications in the middle of recording in application mode. As such, I'd consider this a bug, and a pretty frustrating one at that, given that I basically have to re-record my ~2 hour session.