I think I know what happened. The creeper from other cells has moved to the first ones up to 5M strength, as much as the pin field can handle for moving. I consider this a map editor glitch, because nobody messed up my files...
EDIT: Okay, I hope it was an one-shot glitch, still kinda weird. I'll post the fixed version tommorow, because it's a bit late for me to beat that map again.