Regarding attacking infrastructures, the last time I checked the behaviour was that sending an attacking infrastructure in an undefended territory conquers the territory; instead, if a battle is done and both attackers and defenders are destroyer, attacking infrastructures are conquered by the defender.
I think this should be harmonized, in that either the attacking infrastructures conquer the territory in both cases or are gifted to the defender in both cases.
I think an attacking infrastructure alone should not conquer a territory, but getting conquered, in doing so.
I've not tested this behaviour recently.