When I was playing in a redstone ready world while there was 2 songs were playing at once thankfully giving me a headache, I ran into a zombie with incorrectly textured leather armor. I think it is a resource pack bug or just simply Minecraft making glitches... I can't play on Multiplayer servers so I am not sure about that....
By the way, I am using pure vanilla 1.7.2 downloaded fresh and hot.