skins were disabled in classic...

If you are going to say something like that, provide a link please.

Here is my understanding of what happened.  The same change that broke World of Minecraft's login as well as all of the server software's heartbeats (i.e Minecraft.net has changed its urls from http://www.minecraft.net to https://minecraft.net) with minecraft.net has caused the error with the skins as well.

 URL localURL = new URL("http://www.minecraft.net/skin/" + this.a.name + ".png");

^That's the mojang code from World of Minecraft, the 'www.' is what I believe is breaking the skins.

As simple as a fix as this was for the server softwares, (I know, I made the change on mcforge, it was a one line change), there are quite a few lines of code in World of Minecraft that were broken by the url change (and no, as far as I know, the change was not made in order to kill classic, the hiding of the list a while back; however, was).