[MC-59259] Breaking block below tall plants causes them to drop two items

When you break the block under double tall grass you get 2 double tall grass essentially getting infinite tall grass

Environment

Java: 1.7.0_51, 64-bit operating system, windows

Confirmed.

Also affects double-tall flowers.

Kumasasa: This issue is about breaking the block beneath the bottom block of the plant, not the bottom block of the plant.

Fixed in 14w30a