I agree with Carrie on this one. I believe leaning is a sign of control and dominance, not necessarily aggression. The first time I noticed my black shepherd leaning was at dog obedience. It especially happens when he does not want to obey a command. I will tell him "sit", and finally he will but will lean on my legs as he sits. In this context it is a sure sign of dominance as I can tell he didnt want to listen to me but did reluctantly. Now that it is confirmed that leaning may mean dominance I will alter that behaviour. I found this leaning behaviour strange and now it makes sense.