Update by [Mojang] Mega_Spud (Jay Wells):
Water flowing over mycelium doesn't cause it to turn back to dirt. According to the wiki, it should: "Mycelium reverts to dirt when covered by one of the light-impeding blocks above and the light level at that block is below 4."
Steps to Reproduce:
- Place a bucket of water down on some mycelium
The mycelium does not revert to dirt when under water, at night.
It should turn to dirt, just as grass does when under water, at night.
Screenshots/Videos attached: Yes
Flowing water and water source blocks don't cause Mycelium to turn back into dirt at night.
If you have water flowing over mycelium at night it never changes back to dirt, I was able to recreate the bug both on a flat world and on a vanilla survival realm.