When sneak+scrolling to switch Tinkers tools with only one stored tool, the stored tool will duplicate itself. Basically, the stored tool stays in the storage slot, and a copy is moved to your inventory, and both tools are completely functional and carry the same data. Not that I mind this bug very much, but it's still a bug!

That's a nasty server-communication bug that I'm trying to squish...

Correlate with #56

I would like to say more about this: When you have, for exemple, an item in hotbar at the slot 1 and a tool (even vanilla not necessary tinker) at the slot 2, and you are in slot 1 and shift + wheel down very fast, it duplicate the item (slot 1) by remplacing the tool (slot 2) into the backpack's tool slot. So you got the same item from slot one into backpack's slot tool.