Removing the block below seagrass doesn't cause the seagrass to break

Steps to reproduce:

1. Put water somewhere;
2. Place down a seagrass there;
3. Remove the block below

What should happen:
The seagrass is destroyed.

What actually happens:
The seagrass stays there.

 

This affects double seagrass as well, and removing the bottom part/top part won't destroy the other part.