Weeping Vines cannot be grown using bonemeal and dispensers

Dispensers cannot grow weeping vines using bonemeal.

Steps to reproduce:

1. Place a weeping vine on the underside of a block with space underneath.

2. Place a dispenser facing the weeping vine and load it up with bonemeal.

3. Power the dispenser.

Outcome:

The weeping vine does not grow. Bonemeal is consumed and green particles appear.

Expected outcome:

The weeping vine grows downwards.

Note that manually using bonemeal on a weeping vine works properly.