Chunks sometimes are dislocated / copied to another location

I have played in this single-player world a few times and every time i log into it, i copies and pastes a chunk somewhere else. the house on the left, i did not build. it is a copy of the one on the right. I don't have mods installed or anything. Anyone else having an issue with this? if so how do I fix it? or is it a bug with Minecraft that they will later patch?