Cactus flowers can visually 'float' on top of a wall when the block state 'up' is false. This is usually created when a wall is between two other walls. When this block state is false, the wall no longer provides center support to the cactus flower.

Steps to Reproduce:

1. Place three walls in a row
2. Place a cactus flower on the center wall
3. Watch as it 'floats'

Expected Result:

Either when a cactus flower is placed on a wall, the block state 'up' will be set to true, similar to how torches are when placed on walls, or cactus flowers shouldn't be placeable on walls in this state.

Observed Result: