As we know, we can easily dupe items in Diablo1: just take anything from inventory while picking up an item from a ground and you get two identical items.
HnH works directly opposite — when you are going to pick up an item with a full inventory and on the way make your cursor slot occupied (and inventory is still full), the picking up item just disintegrates.
Encountered this taking off the saddlebags, but it works with an item on the ground too by shift+clicking it.
Had to sacrifice second saddlebags to reproduce the bug: https://files.catbox.moe/u8yoxc.mp4