The bug

When breaking a huge mushroom's stem with silk touch, it correctly drops the "mushroom stem" block. However, when this block is placed and broken again, it drops a brown mushroom block.

How to reproduce

1. Plant either kind of mushroom
2. Bonemeal it to make it huge
3. Break the stem with silk touch
4. Place the obtained stem blocks
5. Break them with silk touch
   →  They drop brown mushroom blocks
6. Break them with your fist
   →  They drop brown mushrooms sometimes