Although LiveJournal and other LiveJournal (LJ)-type systems share similarities in application & source code, each system is a separate entity with its own set of users. If, on LiveJournal, you add an user with the same username as that of another LJ-type system, chances are you're adding someone that has no bearing to the user on the other system. There are cases where users obtained usernames that are identical among the LJ-type systems but the systems do not share any dedicated connection that automatically transfer data among each other.
Past Requests
http://www.livejournal.com/support/see_request.bml?id=26750
http://www.livejournal.com/support/see_request.bml?id=34314
http://www.livejournal.com/support/see_request.bml?id=34870
http://www.livejournal.com/support/see_request.bml?id=36622
http://www.livejournal.com/support/see_request.bml?id=41142
http://www.livejournal.com/support/see_request.bml?id=43393
http://www.livejournal.com/support/see_request.bml?id=52305
http://www.livejournal.com/support/see_request.bml?id=52516
http://www.livejournal.com/support/see_request.bml?id=52767
http://www.livejournal.com/support/see_request.bml?id=53624
http://www.livejournal.com/support/see_request.bml?id=53683
http://www.livejournal.com/support/see_request.bml?id=54271
http://www.livejournal.com/support/see_request.bml?id=58526
http://www.livejournal.com/support/see_request.bml?id=58585
I welcome any thoughts to this.