For many years the developers of Mac for Powerpoint have somehow overlooked a really troublesome glitch which interferes with the switching between PPT documents:

Scenario:

There are one or more PPTs in full-screen mode; and one or more PPTs as a norrmal document window, floating on desktop.

When having played a full-screened PPT's slideshow to view it, after pressing ESC, the other document(s) will also then suddenly be in full screen.

Not only does this cause chaos to the organisation of all open applications, putting numerous PPTs next to each other in full-screen-mode, which is often undesirable and very awkward. But it also is very dangerous for encouraging editing the wrong files and causing confusion, esp. if you have 2 similar PPTs open. This has been the case for me on many occasions and I have to really think about which one I'm editing. Because, if they are all then in full-screen, how do you tell them apart? Looking at the thumbnails in mission-control view is not always helpful/practical.

Microsoft, do your testing, do your homework. This has been going on for such a long time, about 5 years or so if I remember correctly. This problem has happened on both of my Mac computers which I had in that time and it's about time it is dealt with. It is staggering that it's still not fixed!