I went to a jungle, looking for the new bamboo biome, only to find it completely full of mobs, even though it was daytime. I've added some screenshots: the sky can be seen at their top, and I think it's visible enough that there's no obstruction in those areas that could explain their spawning (those areas are so open that those zombies and skeletons should be burning). The third screenshot shows the exact light level on the block where one of those zombies was standing: client light level is 15 but server light level, for some reason, is 0. The four screenshots shows that there's also some strange areas of complete darkness that shouldn't exist (again, there's no obstruction), and have both client and server light levels of 0.