smolki81: Yes! It works! Thank you very much! And Steam community too.
Velgor: It works for me, too. However the mouse still doesn't work correctly when first launched and in the menus. I have to load an old save, alt-tab and then load my current game. Annoying, but at least I can play. Thank you!
Edit: First run thru I could not ALT-TAB out at the first menu, but now I can.
I have an issue with ALT+TAB - very often it crashes the game. Even when on main menu. After I unlock the mouse and it doesn't crash I can play even longer sessions (unless I accidentially hit ALT+TAB, Windows key or any other action resulting in focus loss happens, like notification from external app).
I posted support ticket, hopefully they'll fix it soon.
TheRealDusky: Alt-tabbing just seems to freeze the game when I tab back in. For all I know it fixes the mouse issue, as I can hear sounds when I click the mouse etc after tabbing back in, but the visuals themselves are just frozen.
Try pressing Windows key or ALT+CTRL+DEL. You can also try to ALT+TAB back to the game or click application on taskbar.