Brown mushrooms emit light.

It is an extremely low light level but its noticeable if you are in a totally pitch black room.

Steps to recreate.
1: build a room that has no light at all inside it, no torches, no sunlight, nothing.
2: turn your brightness to max (makes it easier to see)
3: place a brown mushroom
4: it glows.

I did some research on it to mabye answer why or if it even is a bug and i found 0 evidence that this is intended. I did find a page on the fourm that speaks of this and many people say that its a bug that Mojang is either too lazy to fix or hasn't gotten around to it. I did look it up to see if its been reported before and didn't see anything like it. (I searched MCPE Glowing Mushrooms) if this isn't a bug and is intended i would love to know why this is so. Obviously this is a small bug and i wouldn't be suprized if the minecrafters on the fourms were right but unless proven otherwise i see it as a bug. (Yes i did look on the Minecraft Wiki and even they have no explanation at one point even stating that it's a bug)