This incredibly strange lag bug with MCEdit. I MCEdited a completely vanilla, 9x9x10 base into a world. Now my FPS drops from 40 to 10-15 while in this area. Completely lowered settings makes no difference. As soon as I exit the area FPS returns to normal. This makes no sense - I removed every chest, etc. inside the base, all light sources, all possible sources of particles, to no effect.
Anyone having the same issue?