In Creative Gamemode, if i use number key to change item in hotkey slots, they will get back while i place them.

In Creative Gamemode, if I use number key to change item in hotkey slots, they will get back while I place them.
For example, let a stone at the first hotkey slot and a dirt at the second hotkey slot. When I put my mouse on the dirt and press numkey '1', they will change, Now there 'seems' to be a dirt at the first hotkey slot. But while I placed it, the thing I placed became a stone, and the item at the first hotkey slot became a stone, too. The same thind also happened while I placing the stone at the second hotkey slot.