Access Team Issue

Hello,

I'm facing a strange issue with Access Team. In my CRM organization, all opportunities are owned by a Team called "B". If user select the record to be Private, then I use AddUserToRecordTeamResponse to add the record to Access team with its all deal owners and assign the record to Team "C" where both Team "B"(or Business Unit) and "C"(or Business Unit) are under Team(or Business Unit) "A". So "B" & "C" are at the same business level and user can't access the record in cross business unit.

There are no users in Business Unit C and its Team C. But for some reason, some of CRM users can access some records from the access team. I can't figure out how  a user can access the record when his/her BU is totally different then the BU of the record. 

I hope some one might had the same issue and like to know how they fixed it.

thanks