The bug

The heads of pistons are made out of what appears to be oak wood, as implied by their appearance and the piston crafting recipe. Despite this, breaking them, walking on them and so on produces the default block sound - that of stone.

How to reproduce

1. /setblock ~ ~ ~ piston_head
2. Note the stone-like sound when broken
3. /setblock ~ ~ ~ oak_planks
4. Note the wood-like sound when broken
5. /setblock ~ ~ ~ stone
6. Note that this sounds the exact same as the piston head

Expected results

the piston head would make a wood-like sound when broken.

Actual results

The stone sound plays instead.