After it was pointed out by Fred Astair that my Low mini-skirt in "User contributed assets" didn't work, I re-uploaded it--when I updated it some time ago, I didn't update all three of the core files, and so the three weren't compatible, resulting in nothing being displayed when the skirt was selected on a character.
I've also uploaded an additional update (Fred, you won't have this one yet), which adds (teeny-tiny) edges between the front and back faces of the skirt--you wouldn't have noticed these were lacking unless you tried to run a cloth simulation on it, at which point you would have had the front and back falling apart as if they were two separate pieces of fabric, rather than two sides of the same piece. (Note that you don't have to download the diffuse image files again--I kept the same UV maps, since the edges in question are so small as not to show up onscreen.)