[Image: http://puu.sh/7bTl7.jpg]
I tried on every robe I had with a pair of Royal Knight Greaves, and none of them look like they're cutting the boots. If they do, I can't see it because most robes seem to be longer than the Mysterious Robe, so anything cut off would be hidden anyways.
It must be certain footwear then, because I know for certain robes do cut off. Tarlach is a excellent example.
Wave Pattern Boots (No Gloss) cover his hairless legs
Thin Leather Shoes do not cover his shameless sexy legs.
How I know this? Try running with the two on. Thin Leather Shoes you can see your legs while walking/running.