When you first start up 13w24b, it has no resource packs, and starts with the default. once you use the nifty download from [mojang.com] webpage, it translates all your texture packs into resource packs; However the selection on these resource packs is extremely buggy. it starts out selecting default, and show default when you play, but once you pick a resource pack, in the UI it will continue to show that you have default selected, however, once you start playing again, it displays the resource pack. if you happen to want to switch back to default, since it displays that you are using it, it wont properly load therefore making it impossible to go back to default without switching snapshots.