if it wasn't same number, for example 6/6 or 10/10 before you made it unbreakable, then it will show up as repairable. So, if you made some armor that was 1/34 unbreakable, then try to destroy it for a crystal, you will have a reduced chance to get a crystal. If you repair it, it will be 33/33 durability, but unbreakable.