Syntax question: use of join/using with fully qualified table name

I've got a join where a certain column name appears twice:

select username,last_name from eg_member join eg_membership using
(member_id) join eg_account using (account_id) join eg_person using
(person_id);
ERROR: common column name "person_id" appears more than once in left table

My first inclination was to fully quality the table name. Why would
this not be acceptable syntax?

select username,last_name from eg_member join eg_membership using
(member_id) join eg_account using (account_id) join eg_person using
(eg_member.person_id);
ERROR: syntax error at or near "." at character 145

Of course I eventually wrote it:

select username,last_name from eg_member join eg_membership using (member_id) join eg_account using (account_id) join eg_person on eg_member.person_id=eg_person.person_id';

PostgreSQL 8.1.9 on i686-redhat-linux-gnu, compiled by GCC gcc (GCC) 4.1.1 20070105 (Red Hat 4.1.1-51)

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