I'm reporting this in a separate thread so that there is less chance for my report to get lost within the main thread.
My keyboard has an Fn key which, combined with the various F-keys in the upper row, can perform a variety of actions (controlling volume, media playback etc). For some reason, when I use such a key combination, it also causes OXCE to select the next unit on the battlescape. This happens even with the default configuration settings (I deleted my OpenXcom folder in Documents to verify the bug).
In addition, with my configuration file, each time I use an Fn key combo, the whole battlescape suddenly acquires a weird green tint (sorry, I have no idea what this is supposed to be - see screenshot). When I use such a key combo again (not necessarily the one I used just before), the tint disappears.
Also, I have a separate USB volume control with a big knob, and it also cycles through units each time I use it. But all this weirdness only seems to happen on my desktop PC and not on my laptop for some reason. I can provide detailed system information if necessary. My OS is Windows 10 x64, on both PCs.
The bug does not happen in OpenXcom nightly openxcom_git_master_2020_03_27_1613, only in OXCE (6.4.2 tested).