Renamed tool rapidly increases base value each time repaired on an anvil.

I Have an efficiency 5, fortune 3, unbreaking 3 pickaxe named "Speed Miner" I use to mine in my survival. With the new snapshot, at first it only would cost a few levels to fully repair it. The cost for repairing it went up dramatically each time I repaired it even though it was named. I thought renaming it would stop this? Is this a bug?