I also have just joined the forums to follow up on this issue. I just recently started having a similar issue, and I am baffled. I was running a modified Mindcrack 8.1.1 just fine, until i updated mystcraft to 0.10. I also had Divine RPG installed, at this point, my worlds started leaking. So after much fiddling, I decided to cut my losses and start anew. So I have been working on a Mindcrack pack with a good bit of mods added in it. But, the weird thing is, is that I add mods one at a time, and lets say I had such and such mod, it causes world leaks. remove it, start a new world, still have world leaks. completely delete and reinstall Mindcrack, and add that mod right back in. No world leaks. Then I would add a mod that never gave me a problem before, and now I would have more world leaks. It seems it is happening at complete random. I had a very large pack built up, until I added a couple mods and even after removing those mods, I still have world leaks. The weird part is, is that now I cant even run a clean, un-modified Mindcrack without world leaks. Even after completely deleting it and redownloading. I have no idea what is causing this.