When using /auto and picking up and item, for example, Iron ore and it's already in your inventory and your inventory is full it will just drop it on the ground. You can reproduce the bug by doing /auto and filling your inventory with an item and trying to mine the same item. I tested this already on potato and it does the same on the beta server. I came across this while mining for iron on the beta server and I had my inventory full of iron so I would only pick iron up.
