When playing as Aqua u can see the Prince's Cape in the dungeon but he is wearing it when u fight with him WTF

I am going to take a guess that you meant "can't" instead of "can". If so, that is interesting, maybe they just forgot to or something I don't know, but it obviously doesn't have to do with the reason that they took away the capes from the trio's Keyblade Armor.

Here's a thought: he put it on before they ran out into battle.

Maybe that's right, Reversal. Come to think of it, doesn't he put on his cape before he goes to fight in the Sleeping Beauty movie? (It's been awhile since I've watched it, so I could be wrong.)