(Bug happened on an multiplayer server) I had a whole armor with Mending and a sword and an pickaxe with Mending in my inventory and the durability of my pickaxe went down as I mined Nether Quartz Ore. The armors durability was full. I also gained levels during mining. I think this happened because The random selection of an item with Mendig to repair chose an item with full durability and didn´t choose another item after this, but gave the xp to me.