Players can reduce the total weight they're carrying to 0 (or less, unsure if client displays negative numbers in status window?) very easily by following the below testcase.
Testcase:
1. Log in
2. Equip a pick-axe
3. Mine somewhere so you get some ore
4. Place the ore on the ground
5. 'SET AMOUNT 2000 on the ore
6. Attempt to pick up the pile of ore and observe that the server (or client, or both) won't let you
7. Now attempt the same a second time, only this time click somewhere on the ground near your character very rapidly after clicking the "Okay" button when specifying the amount of ore to pick up.
8. Observe that the pile of ore will be moved to the location you clicked, and the total amount of weight your character carries will be reduced to 0 (or less?)