user confusion

Hi

This might be a common error/misconfiguration, but i've been unable to
locate it in the archives..

Using 5.1-RELEASE (upgraded from 5.0 through buildkernel/buildworld).

I'm seeing the following "strangeness"

I login as a normal user, run who .. shows my own username as logged in.
su to another user, logout (back to my own uid), run who, and "su'ed" user
is still listed for my session.

Here's a little "screenshot" (names have been changed to protect the
innocent :* )

-bash-2.05b$ w
11:09PM  up 2 days, 11:27, 2 users, load averages: 1.19, 1.17, 1.16
USER             TTY      FROM              LOGIN_at_  IDLE WHAT
test1            p0       xxx.xx.x.xxx     11:09PM     - w
-bash-2.05b$ su - test2
Password:
Last login: Thu Mar  6 18:39:11 from something.somewhere.
-su-2.05b$ w
11:09PM  up 2 days, 11:27, 2 users, load averages: 1.24, 1.18, 1.17
USER             TTY      FROM              LOGIN_at_  IDLE WHAT
test2            p0       -                11:09PM     - w
-su-2.05b$ logout
-bash-2.05b$ w
11:09PM  up 2 days, 11:27, 2 users, load averages: 1.22, 1.18, 1.17
USER             TTY      FROM              LOGIN_at_  IDLE WHAT
test2            p0       -                11:09PM     - w
-bash-2.05b$ who am i
test2            ttyp0    Jun 12 23:09

----
uname -a gives the following :
FreeBSD some.where.com 5.1-RELEASE FreeBSD 5.1-RELEASE #16: Tue Jun 10
11:24:37 CEST 2003     root_at_some.where.com:/usr/obj/usr/src/sys/KCONF 
i386


Any ideas ??. thought i'd run it though -current before submitting to bugs.

Jimmy