David-
Editing that particular parameter away from the stock size is what fubars the door.
I've tried that at the spring height and at the total height, and have edited the transom height... nothing appears to bring the arch-top transom back into reality. Editing the transom height first turns the door into an error message.
I just discovered "shoulder height" at the top of the whole parameter list, but it's still screwy (tho perhaps less so...). I've set the hole height at 10', the shoulder height at 9', and the transom height at 1', and the preview is still askew.