I've noticed this problem now for well over 2 years on both my desktop and laptop computers.
The problem: After my display engages a program in exclusive fullscreen, some of my other applications that were maximized will then be unmaximized.
What boggles me is how inconsistent this issue is. The things I could learn over the past couple of years after real-world use are:
It happens whenever the display engages a program running in exclusive fullscreen, so both starting up a program in EF or simply alt-tabbing out and back will trigger it.
As far as I can tell, any program running in EF will trigger the problem, though my tests are limited to only a handful of games: WoW; Overwatch; CS:GO; Paladins; Diablo 3; osu!.
Only certain maximized programs are affected, and the programs vary between my desktop PC and laptop PC. On my desktop, I think it only happens with Remote Desktop, while on my laptop it happens with Chrome.
The problem may or may not occur depending on each individual boot. Sometimes I boot the computer and it never happens even after I keep testing to see if it eventually will, and sometimes I boot and it happens every time even after I keep testing to see if it will stop. I don't have statistics, but I'd guess at least 90% of boots experience the problem.
It does not appear to be tied to any graphics driver nor GPU manufacturer as the laptop is running on an Intel iGPU (6200u) and the desktop has been through both AMD and NVIDIA GPUs (280X and 1080Ti), drivers on both computers were always updated to the latest ones every 2 months on average.
I've only tested in Windows 10 so far, but I've gone through several build versions (from RS2 to RS4) in both computers and the problem has always been present.
Over the years I've looked for answers on Google on and off but never found anyone with this particular issue, so I am really out of ideas.