as video_window already sets the window size excluding the window border.
Manual:
When the border style is changed,
the size vector should also be set
to the current engine resolution (screen_size).
Otherwise the window will keep its previous size,
but due to the changed border
the inner client area has now a different size and will appear distorted.
If I understood it right, the window_size includes the border.
The problem is just, that this suggestion with "screen_size" doesn't work. -.o'
