In 1.7. When you drop/pickup the same item, it will do it with no visual action.
In 1.8 Prerelease, if you pickup an item that is the same, it makes the hand go in and out for a second, same with spamming q to drop the item.
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Still in 16w42a. Not sure, but this might be intentional. I personally prefer the current behaviour.
Still occurs on pre-2
EDIT: Can confirm that this has happened since 14w25b