Giant mushroom stems do not drop the block with the right datavalue, but the block of the giant mushroom itself

*What I was expected to happen was that the stem of a giant brown mushroom dropped a block with a mushroom stem texture (block 99:10).
*What actually happened was that it droppes a block with a fully brown texture (block 99:14) like the rest of the mushroom.
Bug is with both the giant mushroom colours

Steps to reproduce:
1. Make an silk touch tool.
2. Place a brown mushroom in a dark spot on top of some dirt with a lot of room above it.
3. Use bonemeal on it.
3. Chop the stem down and notice that it drops the wrong block