There was lot of interesting levels you could make because of the flaws.
I don't think I'd call those flaws, so much as artifacts. For those not familiar, Descent used a portal based engine, but unlike today's portal engines where a portal links a room to a room, Descent's rooms were made out of many 6-sided polyhedrons (aka cubes, even though they could be deformed beyond cubiness). Each face of the polyhedron could be textured (to form a wall) or be a portal to the face of another, arbitrary, polyhedron, anywhere in the level. I forget now if the level format supported self-referencing (eg, a face that links to itself or to another face on the same polyhedron). The editors usually made it hard (but not impossible) to pull some of these tricks, but the raw data supported it.