This one is is Hold steady true: units align themselves to the Transport's heading and ignore any hierarchy turning, even from their attached pieces. For example the infantry unit is attached to the turret that is turned to the side, yet is faces forward and does not respond to the turret's turning.
This one is hold steady false, it aligns to the map??? So when your transport turns all attached units stay facing the original direction.
edit: Please move to Dev requested features. I and other mod/ game dev's could use a functional attachment system, a third option for holdsteady would be fine, as long as it allows for movement and rotations of attached units, if it is not too much to ask for.