Anvil Glitch

So what happens is i try and combine two diamond swords one with knockback 2 and and smite 4 and one with just smite 4. It cost 16 levels, so it took the exp away and put the sword in my inventory. Then i look at the anvil and my two swords are in front of it. So i look in my inventory and then my newly combined sword is gone and so is my exp. But the next time i earn exp it brings back the levels i lost from combining those two swords. This is a glitch with the anvil because i try and rename anything an it will glitch and take my exp but not give my renamed item. But same as before the next time i earn exp it gives me back my levels from renaming my item. This glitch only happens on multiplayer and not singelplayer.