There is a graphical bug with the Archmage robes and a few pairs of boots (Thieves' Guild, Thalmor, Elven) that makes a segment of the player's legs vanish when they're worn together, specifically the segment that was, in Morrowind, called the knee. I downloaded the Creation Kit to have a look at the items in question, but the way body parts are handled in Skyrim seems to be so wildly different from how Morrowind does it that I couldn't figure out anything from that. The nature of the problem suggests it may be an issue with the 3D models themselves, but given the difference between Morrowind equipment and Skyrim equipment I can't be sure.
Any clothing/armor modders have an idea of how to fix this? I've Googled for a fix but can't find one that exists.