Giant spruce trees generate incorrectly

When grown with bonemeal on floating grass, there is a chance that the leaves will generate below the level of that grass

Steps to Reproduce:
1. Place a 2x2 platform of dirt some height above the ground
2. Place 4 spruce saplings on the dirt
3. Spam with bonemeal

This may require some repetition, because it only happens with the 'conical' spruces.