I think the bigger question is why was the jetway retracted in the first place. Normally, when you request deboarding, it would ask you what you want to do with the jetway, and it would position the jetway before the deboarding starts. In any event, I'm not sure why you think it's a bug that the jetway can't be operated with deboarding taking place. If it allowed you to operate the jetway as you please with deboarding taking place, what's stopping you from pulling the jetway away from the plane as passengers are exiting the aircraft. Bad things would happen if you did that.
