What I expected:
When in Creative mode when you mouseover an item/block from the list (or anywhere in the inventory) and press 1-9 the item gets moved with a full stack to the according button position.

What happened:
When I press 1-9 a stack is sent/moved but when I place the block, it depletes (even a full stack) and the block/item in the inventory and the world gets replaced with the previous block that was there AND the moved block also reappears in the old position.

Example:
(2) is Stone Brick Stairs, (1) is Stone Bricks.
Mouseover (2) and press (1)
The Stone Bricks move to (1) and the Stone Brick Stairs moves to (2)
Place the Stone Brick Stairs (1)
Stone Brick Stairs get placed but they are immediately replaced with Stone Bricks (previously 2) in the world and in the inventory, the Stone Brick Stairs also revert back to Stone Bricks so in the inventory you have Stone Bricks in (1) and (2)

This bug was present in older version of the snapshots as well.