Well, I have deemed the cave to be cursed. To update the situation from my previous post: I logged back in today, the zombies were still there, it was still laggy, and I died instantly. I died about a dozen more times trying to get my stuff back and I still lost my original diamond sword. I made sure the whole dungeon was lit up and the caverns around it are completely lit. The dungeon itself is closed off and empty.
Infinite amounts of zombies still spawn from it, even now. Coordinates are -752, 10, 1441.
I recorded a video and uploaded it for download. "Save as", please.
After watching the video, can an admin please tell me WTF is going on? Honestly, this kind of BS has cost me basically diamond block in just a week.