Doesn't happen with all items, I tried to make some lockpicks disappear while picking up a shield two tiles away, but most other things you can pick up off the ground and do magic tricks with. (EDIT: as I mention below, inventory was full when this happened)
Does it just 'disappear' or is it destroyed? Because I am aware that there are things you can do that make items 'temporarily' disappear, but what actually is happening, is you are seemingly holding two items at the same time (I think it's just a method of juggling items in your inventory when you have one too many). I THINK I've seen what you are talking about, and if so, it's not a bug.
I'm not able to find it. I can pick an item up off the floor and juggle it with the mouse, then try to pick up something else and the first item will disappear. If I put the other item down, I'm not holding anything. I'll have to check that game again, and see if my inventory is full. I'm not able to reproduce it on a clean new game.
Okay, it looks like this only happens when the inventory is full. It looks like I just destroyed a Pear Brandy while picking up an Ingot Grinder.