Thank you very much for your report and comment regarding this issue!
As far as I know, this is a limitation of how Archicad display windows contours in 2D in case the frame thickness is larger than the wall thickness. Could you help me to understand why this is necessary? In reality, usually, the wall is thicker than the window frame. The casing is a different part and can be set independently from the window frame.
Looking forward to hearing from you!
Technical Support Engineer