Oh I see the resize function does a cropping unless I choose stretch (as it was a noise texture I didn't notice).
But nonetheless, It's still kinda weird to keep the old big collision poly. Maybe it would be better to add another option that says "scale/trim/don't modify the collision polygon accordingly".
I think for most case I would scale it. But it would at least make people aware of what the resize will do.
As we don't see collision polygons by default we might miss the consequence of a resize and come across unexpected bugs.