Hi, it's me again, back with the Potato Furnace.   So, I have the furnace functionality working (just whatever you do, do NOT move/drop/touch the item in creative mode while it has items in it).   If you download the mod (diamond2potato-1.0.jar or build it yourself), load it up in a singleplayer (or multiplayer, it works in both) world, run the /pfurnace command (for testing), and open the GUI, you'll find that the item you opened the GUI from is somewhat hard to move. You ca