Hello everyone, i recently just updated my spigot server to 1.7.8 then i went into my world, well i went out like 500 blocks from spawn and all the sudden it drops down and its a superflat world all of the sudden...and it does this all the way around..but the inside of it is biomes...ive tried going back to my old spigot version and using an old backup that was saved yesterday...its still doing it...i dont really want to create a whole new world again if anyone can help me. thanks.
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here is what my world looks like in the mapviewer the server uses. 
