PowerPoint, when exiting Slide Show view, always jumps to another window

This is incredibly infuriating.

I have two slide-decks open: one I'm working on (A), and another I'm referring to and copying slides from (B).

Whenever I play the slide show for A (to test out animations or see how a slide will look when presented) and then exit the slide show to edit A's slides, PowerPoint will always jump to slide deck B, forcing me to manually switch back to slide deck A so I can continue editing. I never edit B, I never save it or update it or modify it in anyway; I've tried opening it after I open slide deck A, tried closing all other slide decks besides A and B, tried minimizing it, but Power Point will always switch to B whenever I exit A's slideshow. Strangely, if I present B and then exit it's slideshow, PowerPoint will automatically switch to A. I've tried opening up other slide decks (let's call them C and D) to see if, when I exit their slide show, they'll also jump to B - they do, every time. If I close B, then after exiting A's slide show it will jump to C or D. So the general issue seems to be that, whenever I exit a slide show, PowerPoint will always jump to another slide deck if more than one is open.

It only takes me a second to swap back to A, but when you're fine-tuning a slide-show this can quickly add up to minutes - not to mention there's no rhyme or reason to it so it quickly becomes frustrating having to constantly wrestle Power Point to do something as simple as let me edit the slide deck I was just presenting, the only slide deck I have edited, the only one I ever start the slide show on. It's as if Power Point knows I'm working on this specific slide deck and is going out of its way to make it harder for me to do so.

I've had this issue for months now and have been able to grit my teeth and put up with it, but I've finally gotten so fed up I'm willing to try my luck on here. Google hasn't helped.

I'm using Microsoft PowerPoint for Mac v16.42, on a MacBook Pro running MacOS Catalina v10.15.6