Joshua Fiser
Assigned
Reported
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I have just encountered this bug as well. Been playing Minecraft for years, no issue, but on a new map my girlfriend and I made and play LAN on.
It happened the first time I built a nether portal. I died in the nether and upon return to the Overworld, a tower I built to be the "center" of our map was just completely gone. It appears to be any time one of us leaves and goes to the nether. I tried building a nether portal way far away on our map, think it happened where the nether portal was, but the tower disappeared again. Next I thought it might have to do with dying in the nether, but just tonight we went into the nether, didn't die and returned. The tower is gone again, the nearby Village has the strange textures being replicated upward thing you mentioned, and three full chunks of the rather large castle I made are gone as well.
All of the missing parts are back to the default seed value. part of the village disappeared in the same way.
So far though, it only seems to happen when we travel to the nether and back.
I can fairly easily replicate the issue (it happens at least 80% of the times someone visits the nether, presumably any trip to another world). I've also uploaded screen shots of it in my 1.5.2 world (All of which is a result of the last time the bug happened, our last trip to the nether on 5/8/13).