I haven't done extensive testing, but I know Brown Mushrooms act weirdly around fire, and I don't believe this is intentional.
In the video I attached to this report you see me perform two actions:
In the first part, you see me placing mushrooms on some netherack in the nether. In the middle of this square of mushrooms, I light that block on fire. Nothing happens until I then extinguish the fire, and when I do all adjacent mushrooms (even the diagonals) break along with it.
In the second part, you see me lighting some netherack on fire and attempting to place mushrooms around it. However I can't, and it isn't just all the adjacent blocks, it's more of in a circle shape where I can't place them.
Further testing will need to be done to see what other blocks are affected by fire.
(Nvm just going to link the video to a streamable page since there is an upload size limit, but it's otherwise the same video)
Mushrooms can only be placed in certain light levels, and drop if the light level is too high.