I don't know if this is really a bug, but it is something that can be abused, and perhaps ought to be changed.
We have an achievement called Treasure Hunter, which gives bonus to luck, and it is leveled up by collecting items on the ground. You can actually level it up simply by dropping items on the ground and then pick them up again. If you have 10 or so items in the inventory, which you continuously drop and pick up, then it goes pretty fast.
Could it possible be made so that an item only counts the first time it is picked up, or alternatively that 1 is subtracted from the count every time we drop an item?