I tested it out on a separate Windows 8.1 machine, and the behavior is slightly different this time. Instead of going full-screen, the window instead goes borderless and then jumps to the top-left corner of the screen. Pressing F11 again will put it into full-screen mode, and pressing it again will take it back out, except the window remains at the same size as the monitor (it just adds a border). From thereon out it will switch in between the two without jumping to the top-left like it does on the first key-press.
Maybe my development environment across both machines is acting up for some reason. I'm using VS2015 on both, with Visual C++ 14.0. I haven't tested other compilers just yet.
Another thing I tried was using the same executable, compiled on one machine, across multiple different machines. Regardless of which one it was compiled on, the same respective problem occurs for each Windows 8.1 machine (that is, they all exhibit the problematic behavior with their own consistent quirks). So, this leads me to believe it's not a compiler issue.
Also, I tested that same executable on a Windows 10 machine. The problem did not occur this time, so it seems restricted to Windows 8.1.