When destroying one block of tall seagrass, the other block becomes air when destroyed, rather than water

The bug

Basically MC-125212, except it's only for the one block of tall seagrass that isn't destroyed by the player.

How to reproduce

1. Put seagrass underwater (the water should not be too shallow)
2. Use bone meal on it, so it becomes tall seagrass
3. Break the higher of the two blocks comprising the tall seagrass
   → For a brief moment, the lower block becomes an air block instead of a water block

Small dripleaf fixed in 21w20a.