[douglas]

There are exactly two ways to get ships past a minefield without sweeping or triggering the mines - get them there before you break your treaty with whoever controls the minefield, or get them there before the minefield exists. If an enemy fleet moved into a square with a hostile minefield in it and the mines are still there after the fleet moved, you encountered a bug. Mines launched after the fleet has already arrived will not detonate, nor will mines that were present but didn't blow immediately due to a treaty, but any time a hostile ship moves into a pre-existing minefield the mines will blow, even if the ship is cloaked beyond your ability to detect normally.