When I go to repair an enchanted item, ie sword, helmet, etc, with a standard version of the item both items return to my inventory unchanged and it takes my XP until I kill an enemy or mine ore then it returns to the previous level.

Ex: Player Level 9.5

Diamond Sword with Sharpness 3 + Diamond Sword + 7 Lvl= Sword with Sharpness 3 + Diamond Sword and I am Level 2.5. Kill a skeleton and then I immediately become level 9.75.