This happens to every single block/item:
If you want to move stuff quickly in your inventory in creative mode, you can press the Hotbar slot (a number here) button and it will move the block in you inventory, but if you actually place it on somewhere, it turns up to be the block you just moved and get you a clone of the block you moved.

What I expected to happen was....:
The block/stuff should change the order and so i can use it really easily

What actually happened was...:
The block actually get cloned and both slots are the same block.

Steps to Reproduce:
1. select two different blocks/things in your random two hotbar slots
2. and then put them in it
3. now press the hotbar slot button (like 1 and 2, but press the hotbar slot 2 when your mouse is on top of the block that is in the hotbar slot 1)
4. The bug should be triggered and it should happen!