2 block tall flowers generated in previous version removes the 2nd block

2 block tall flowers generated in previous snapshot removes 2nd block in 14w29a

What I expected to happen was...:
There would be a normal 2 block tall flower there.

What actually happened was...:
The top block was missing.
(I placed the normal flower in the picture)

Steps to Reproduce:
1. Go to a previous snapshot.
2. Place a 2 block tall flower.
3. Go to 14w29a.
4. The top block of the flower you placed should be missing.

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Other steps to Reproduce:

1. Create a new world in 1.7.10
2. Place some 2 block tall flowers, ferns grass
3. Go to 14w29b.
4. Placed tall flowers drop as item, fern and grass vanishes.
5. Double tall grass and sunflowers placed by world gen are not affected.