Put the summary of the bug you're having here

I would place a block

I clicked to place a Quarts block and it disappeared

1. Put item in slot 1 in your hotbar
(exit creative menu)
(enter back into creative menu)
2. Hover over the item
3. Click 2 on your numberpad
4. It will move to slot 2 in your hotbar.
5. Hover over the item again.
6. Click 1 on your numberpad
(exit creative menu)
7. Try and place the item. It disappears!!!