If you make a brute, whether it be a pupil or a master, that brute is set to your ip address. So if you go to pupil someone with a brute already set to your ip address that person will not gain exp from the pupil.
The only way to gain exp from a new pupil is to have someone (An Ip) create a pupil with no other brute set to his/her ip address.
What I'm trying to say is...
If that person who pupils you has created a brute already, you will not gain exp from his pupil and vice versa.