Lily pads disappear if placed on tall seagrass

When you place a lily pad on top of tall seagrass, then break the bottom half of the sea grass, the lily pad disappears.

Steps to Reproduce:
1. Place seagrass in water, bone meal it to make it two tall.
2. Place a lily pad directly on top of the seagrass.
3. Break the bottom half of the tall seagrass.