Anvils fail to preserve high level enchants

Given two items:

<italic><rarity:blue>Chipped FlameVenom Fang | Sharpness 1 | Fire Aspect 1 | Unbreaking 5

and combining them in an anvil, the result has

SH2/FA2/UB3 | cost: 30 levels

This downgrades the Unbreaking enchantment.

I propose that when high-level enchants (meaning higher than possible normally in survival) are present on an item, and two identical copies of that item are combined in an Anvil, that:

1. The result is identical to the inputs, durability added
2. The cost is reduced

Or, a second result is available with the above changes.