If you place a lilypad on water, and just after you placed it move your camera to another block of water, sometimes a ghost block lilypad can spawn. If you right click it, it will disappear.

How to reproduce:

1. Place a lilypad on water and don't release right click.
2. Immediatly turn your camera to the block next to the one you placed the lilypad.
3. Release right click.
4. If done right, a ghost block lilypad should be placed.

I provided a video of this bug.