Duplication Glitch

I accidently duplicated my pickaxe. This is how it happened. My pickaxe has mending on it, and it was in my offhand. I wanted to take it out of my offhand while it was being mended by some experience I have gotten from some villagers. Instead of being taken out of the offhand, an exact copy of it has been made instead, and now I have 2 pickaxes. This only happens on mending tools. Once I found the glitch, I restarted the game and the pickaxe has disappeared from my inventory, like it was never there. It gave me a spook, cause I thought i could exploit this but nope. Also the pickaxe doesn't seem to be able to do anything, and if you put the real picakxe ontop the copy pickaxe it just replaces the duplicate. So I am assuming that this is an appearance bug, which seems to duplicate stuff that isn't there, because It doesn't work or anything like that. Please fix this bug, it can get annoying, since I use my offhand to fix mending tools every day!