Sunflower can make gravel float when broken

After destroying the sunflower with the gravel on top the gravel floated (this also works with sand and red sand)

What I expected to happen was...:
The gravel to fall to the floor

What actually happened was...:
the gravel floated

Steps to Reproduce:
1. put down a sunflower
2. ...put gravel on top of the sunflower
3. ...break the sunflower then the gravel will float