So, trying to deepen the analysis of the problem.
That screenshot is actually 1152x864, I didn't see that fact, thanks Suen.
Which is strange, 'cause my in game resolution is 1280 x 1024, BUT my desktop resolution is 1152x864.
This means that even if in game I choose a resolution, that will not affect the game, if it's different from the desktop resolution?
(plus, I've tried to move my desktop resolution to 1280 x 1024, but in game the situation didn't change. Just on the main menu I've got two black band, up and down.)
I suppose this isn't even a known issue, at this point. :/