If the window resolution is larger than the system resolution, it will resize the window to fit but there is an offset equal to the window border + whatever system panels are taking up the desktop area. The offset appears to only affect the drawing because the hit area for the buttons are where they should be.

The offset is fixed if you resize the window however if you change the window resolution it knocks the offset back.

Attached is a screenshot from Uebergame which shows the offset.