Lingering FTP session in Oracle 10.2 XML DB - normal behavior or a bug?

When I start an FTP session into an Oracle 10.2 database with XML DB and immediately simply quit, the session still remains in v$session.  Why?  This does NOT happen when I start and end other Oracle utilities such as sqlplus, imp, exp, etc.  The following dialog snippets will help you understand my problem better.

Before I start the FTP session
SQL> select count (*) from v$session where username = 'TMA410';
0

After I start the FTP session
$ ftp 127.0.0.1  2100
Connected to 127.0.0.1.
Name (127.0.0.1:partha): tma410
331 pass required for TMA410
Password:
230 TMA410 logged in
Remote system type is Unix.
ftp>

SQL> select count (*) from