So, on ItsFundy's livestream last night, he found a bunch of mushrooms on the Nether roof and found one of them being a lot smaller than the others. I'm not sure if this is a bug or not but I really have no idea where else to put this so that someone from the Minecraft team knows about it since I have not found any evidence of mushrooms being different sizes anywhere when searching this up. Why does this happen (and if it's a visual glitch don't fix it this is cool). 

Twitch clip of Fundy finding the small mushroom (file is like 40MB)
https://clips.twitch.tv/ArborealPopularNarwhalPJSalt