Steps to reproduce:
1. Find 2-block high seagrass.
2. Place a block on the lower portion.
3. Break the block you just placed.

Expected results:
When you place the block, it removes both halves of the seagrass.

Actual results:
When you place the block, it removes only the lower half of the seagrass.
After you break the block you placed, the upper half of the seagrass is left floating above the seafloor.