i just tried to reproduce this on .30e without success. is there something more to it you are failing to mention? using both slaves and regular workers i was unable to affect existing developed mana nodes by simply building a road to a developed mana node. both with the node already started but not completed, and with the node already built before telling the workers to start the road. are you certain it wasn't the amurite world spell? what race/civilization were you? anything else you can think of that you were doing?