Enchantments do not combine/level up via anvil

when trying to combine two like items on an anvil the magic does not plus up.

example1: two iron shovels with efficiency II should result in a shovel with efficiency III but currently getting just efficiency II iron shovel.

example2: a silk touch iron shovel plus a efficiency II iron shovel should equal a iron shovel with both silk touch and efficiency II on it. . . . depending on order one of those enchantments disappear