I noticed with the recent experiment skins that only cover part of the avatar, that when I wear those the default avatar base isn't showing up underneath on the site (it does show up in the wardrobe preview). with the 1337 experiment skin that makes most of my face and body essentially see-through, showing the background behind it instead. this also happens in item previews. It appears to be mostly happening with the more recent skins, I just tested the sticky vial zombie skin and that does show the avatar base underneath, but the experiment 870 skin from last year doesn't.