So in the map Nuketown there is a iron door glitched from OITC this was in OITC map 11 or 12 i am not sure wich one ;)
It's a visual glitch, it happens to me when I use Optifine. The door works fine but the textures mess up, one main way I get rid of it is reloging or using normal Minecraft. Someone please correct me if I'm wrong.
I don't use optifine and I still see it that way ;P I don't know if it fixes when you relog, but I guess it wouldn't hurt to try relogging...