I cannot confirm if this is 16.3 or not, however, whenever I open a veterans shop the window forces my "buy" window to only a width of 2 boxes. Since I use shopping with text and not icons this gets pretty annoying especially since you can not stretch the veterans shop window out.
I have no custom gui or 3rd party apps applied or running when this occurs. After opening a veterans shop, all other shop windows are also forced to a width of 2 boxes as well.
100% reproduceable.
1) Go to fair trade in borealis and open up a shop session
2) Format you window how you like it.
3) Go to veterans shop and open trade (window becomes forces to the new sized and cannot be altered)
4) Close trade and return to fair trade
5) Open trade with a shop and the window will be forced to the veteran's window size.