random castle generation, which ended up cutting off part of my castle that i spent many days building. confirmed in 1.5.2 not tested on any other versions to date. listed below is a screenshot, as i cant give a crash report as i dont know when this happened
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Can you provide a better screenshot during day / with night vision?
this is what it looks like in the day time
its just so large, not as large as my other castle but still about 1/4 of the size of the one i built. and thats a good 400x400 area

no, because its simply just a structure that popped up. i have never built anything like this before. and it just sort of showed up...

It's really not clear from your description or picture what the problem is. What did you make, and what showed up that you didn't make? "Castles" do not generate naturally in Minecraft, though NPC villages and Strongholds do.
that castle comes from the "tale of kingdoms" mod, either part 1 or 2.
if you used it at one point, then deleted your world and remade a new one with the same name, it's possible it "imported" some of the chunks that minecraft failed to delete.
the failure to delete existing worlds/saves is a pretty old minecraft bug.
either that or you actually installed the mod into your world which caused this, in which case the ticket's invalid.

The bug which yarrmateys is referring to is MC-315.
You should produce a manual crash report by holding F3 and C for 10 seconds, and attach the file to this ticket.
Resolving as duplicate of MC-315 because there has been no response.