The command /clear is still missing an amount-argument. Even though it has been reported plenty of times.
This makes it impossible to use the /clear command for anything useful, like a commandblock-based store, where you would trade with gold or emeralds, or an adventure map where you would need to have a certain number of an item in order to proceed.

Before anyone marks this as "works as intended" and say this should go to some suggestions-forum, I would like to argue that a bug isn't necessarily that something doesn't work as promised, but could also be, as in this case, a forgotten feature. It seems that the people behind Minecraft simply just forgot to implement this, especially when you can remove a specified number of xp levels.