There are several situations where it simply is not possible to 'let go' of whatever is in your cursor; most notably when in complete darkness, but sometimes when there are just too many items on the ground and you just want to drop the thing you have in the cursor.
I believe that this could be easily resolved by allowing a key to be bound to simply 'let go' of whatever you happen to be holding in the cursor.
I just lost a pretty fun wilderness game simply because I couldn't let go of an item in my cursor to make a torch. Sure you might want to argue that I should have pre-created a torch, but I think that a stronger argument is that it's pretty dumb that you can't just 'let go' of an item 