I've plugged more than a few hours into building a mob spawner-- it was working great, but recently-- as in, even before the update-- the game randomly decides that the entire inside of my mob spawner is exposed to the sky, and sunlight passes through the roof like it's made of glass. I've tried reloading the chunks, replacing the roof, building a second roof above the first roof, all sorts of stuff.

Interestingly enough, although the roof is letting light through, the platform I collect mob drops from isn't, despite that they're built out of the same materials (a combination of polished stone and cobblestone). The ocean, about 128 blocks below, shows the shadow of the platform I collect the drops on, and the platform itself is dark on the bottom, unlike the bottom of the spawner assembly, which is lit up as though it has full sunlight on it. 

I have no idea how to solve this problem, but it's pretty much killed my game experience; I picked the game back up during the 10th anniversary to have some fun and relive the nostalgia, but honestly, at this point I'm mostly just disappointed.