The ghost just kills people in the Dark Forest. I don't know if he gets as far as the dwarven halls, but he will kill the urn hunters and most of the elves in the village.
Try quicksaving before starting the drag and drop to duplicate; ie quick save the game, then drag an item out of your inventory, but not somewhere there is a red X. Without dropping first, quick load the game, then release the mouse button when it starts to load. This should produce a copy of the item on the ground, with the original still in your inventory.
If you try the other duplication trick on a small stack of potions and enter a small negative number, does the game still crash?
Drag a stack out of (or into) your inventory (or container) and hold down the control key before dropping. This will bring up the split stack pane; type in a negative number and hit enter (the checkmark will be greyed out). This can also be done in the trade window.
Both methods should still work in the patched game.
