Will the mouse area be adjusted to change the window size at the bottom right or is the size fixed?
Given the graphic sizes of the corner and scroll bars in the picture, the size change only reacts in a small area in the corner.
(https://forum.simutrans.com/index.php?action=dlattach;topic=21181.0;attach=29951;image)
Should be better in r10159. Size is taken to be maximum of the resizer-image and scrollbar sizes.