ya i think there was some glitchy chunk generation right around the 1.9-pre days, maybe 1.0. It could do things like that, and i seem to remember that it was just a single chunk at a time, or maybe a small number of them that looked out of place. you could probably find some posts about it if you look hard enough.
Although, that does seem more drastic than I remember, so the orc above may be correct as well. If Nork is correct, consider yourself lucky that it isn't more drastic.
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This is just the inside part of the tower, everything else is just outside.
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