Ok, if I understand it correctly:
is one account
has joe@mydomain as a part of the 'group', correct?
Double check the group,
and make sure your account (firstname.lastname@example.org) is NOT in there twice. Also, in that group,
, make sure if there is an ADMIN group, and you're (email@example.com) part of it, then that would be why you'd get it twice...
Sounds confusing, I know...