Can't combine swords/tools/armor with Unbreakable tag in an anvil

If you give yourself 2 unbreakable swords with this command

/give @s minecraft:diamond_sword[minecraft:unbreakable={}] 2

you cannot combine them in an anvil.

This makes it hard in some custom maps to obtain higher levels of enchantments.

Suggested fix:
Make it only possible to combine unbreakable tools with the same damage value, and have the returned item have that damage too (so custom models don’t change and still make sense). Possibly making it a gamerule.