The pictures tell you but I will read it out anyway just in case you cannot read:
1. I place a stone block. It works and the stone block stays in my inventory.
2. I juggle the stone block around in the hotbar in the creative inventory with the 1-9 keys.
3. I place another stone block next to the original one.
4. A tick after I place the block, the block I placed GOES as well as the stone in my inventory hotbar that I was using.
I could not uploud photo number 3 or four due to faults.

I investigated further and found that the "trick" works on any block. I recently tried the "trick" with wool and the wool, as well as the wool in my inventory, disappeared.