I dont know if this is a feature or a bug, but it might be a bug so il send anyways. Red mushrooms/ brown mushroom generating in drops into items when growing on tuff block. Its not much but it really weird for that to happen.
seed:-894938320998262692
coords 206 -9 -253
seed:7753075226904391792 (this msuhroom grow on the tuffblock above and breaks)
coords 241 80 79
Having scoured thousands of blocks in a new world using the commands listed at the bottom of my post, the only mushrooms I found (3) that itemized was due to flowing water. Chances are it was the light from the lava uprooting the mushrooms like in the image I'll upload.
The seeds you provided didn't have mushrooms on my end, probably because seeds don't dictate mushroom spawns.
Commands:
/execute at @e[type=minecraft:item, limit=1, nbt={Item:{id:"minecraft:red_mushroom"}}] if entity @e[type=minecraft:item, limit=1] run tp @s ~ ~ ~
/execute at @e[type=minecraft:item, limit=1, nbt={Item:{id:"minecraft:brown_mushroom"}}] if entity @e[type=minecraft:item, limit=1] run tp @s ~ ~ ~