Phantom user in db--'128'

I posted this earlier, and got no responses.
While using pg_dump and pg_restore (or attempting to restore, more
precisely), the process failed because of a missing user, user '128'. I
never created such a user, and when going to Privileges, such a user does
not exist in the list. However, while going out and checking some of the
tables, this user shows up as a user with privileges on them (however, not
on all tables). How do I get rid of this user? And how do I ensure that it
doesn't get created again? I'd like to understand what is really going on
before hacking the user table.
Thanks in advance.

Mark Taber
State of California
Department of Finance
Infrastructure & Architecture

916.323.3104 x 2945
mark(dot)taber(at)dof(dot)ca(dot)gov