'Frozen Observers'

[purpledragonnuke]

In Forge for Minecraft 1.11.2, if you use forge and then switch back to vanilla, any observer blocks in any single player worlds you loaded will become 'frozen'. They will not output a redstone pulse when they are given the appropriate input. They all have to be broken and placed again in order for them to work properly.

[LexManos]

Interesting this is actually a vanilla world loading bug that we generically fix in Forge. {Illegal blockstates being saved to the chunk data}

It *should* pulse the world and remove it's 'powered' flag. But seems vanilla is broken and doesn't do that.