Didn't feel like playing, but I'll say that on win10, modern AMD cpu n gpu it works fine. Also I'll note that on my 16:10 monitor it put all of the letterboxing on the top, which is something I haven't seen before.
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Just to be clear, I meant letterboxing as in the extra pixels on the top and bottom that try to keep it in 16:9 ratio. Another thing I found out: when in 16:10 the hotspot for mouse-to-button on the main menu is offset, which is probably all related. Didn't notice before since I moved it to my standard monitor and played with it for minute.

Sorry my bad. In that case it works as intended (the grey area should be on the top while the game area should stick to the bottom). For the mouse, I made some tests before for such cases and it seemed to be working for different window sizes. I guess I will have to do more tests. Thank you again for clarifying the issues!