cannot have the same User in 2 different developer accounts

1. create new user in /buyers/accounts - usera with email usera@beispiel.de with new group useragrp
2. login to developer portal(different account than usera and with different organization than usera) and invite user with email usera@beispiel.de
3. usera is not able to accept invitation because usera is not possible to create account because that account already exists. I expect that if account with such email does already exists, it will not show form for creating new user but login page to dev. portal.