Normally it should not go into window mode, may I ask what is your desktop resolution?
Sorry for the late response... I played the whole game. My resolution is 1920x1080
As a heads up, I am experiencing the same problem with the same resolution as him
chachky, I sent you an email.
For what it's worth, I had this problem and was able to fix it by turning scaling in windows down from 125% to 100%.
The same problem
Just FYI, I'm having the same problems - changing the scaling of my pcs hasn't fixed them.