I fixed the noticed bugs and uploaded the corrected version.
That was quick, thank you :) #1 and #2 are fixed for me.
#3 seems to be a weird one, actually. Sometimes (not every time though), when I start the game with "fullscreen" already enabled (from a previous session), the game window is created with an offset of x=36, y=71 from the top left corner of the screen instead of x= 0, y=0 (perhaps the Win 10 default window displacement?). The game cursor is displayed with that same offset, yet the actual clicks are registered without the offset - which is causing the problem I previously described. I don't know whether this has something to do with how Windows launches the game and if another process interferes with this, perhaps stealing focus...