I wanted to turn my map into Winter style and changed the biome to ice plains, I had Lava under glass but it disappears! (Not all at once) I dont think is from Minecraft itself because I found nothing in Google. Here a list of plugins that are possible oft causing this: -Worldguard -Craftbook Thank you for helping!
dav20011 Delete each one and try again. Keep doing this until it works and you know what is causing the problem.
