For some reason the skirts are really glitchy. I fixed them up a bit for the 2.1 patch so they no longer make vertical spinners unbalanced, but they still occasionally collide weirdly. I think I'm going to try just making totally new objects with the same dimensions and see if it helps.
For now I can just suggest not to put too much weight on the skirts; that tends to make them sink into the floor, especially when they're the angled kind and the weight is concentrated on the point.