It was actually also raise in the below posts and never resolved.
https://discourse.mcneel.com/t/wish-box-3point-height-always-in-wcs-direction/127495
https://discourse.mcneel.com/t/negative-height-in-box-3-point-height/70674
https://discourse.mcneel.com/t/bug-entering-dimensions-for-box/70342/6