Old packages not purged after yum update?

Hi,

I have a set of RHEL5.2 servers. They were installed with the exact same
kickstart profile and the difference in setup is purely the time of
install.

During a routine check of the packages installed on a pair of these I
discovered that the "older" server had old versions listed for various
packages, snippet of the diff below :

--- rpmlist.oldsrv	2009-01-08 15:45:05.072961519 +0100
+++ rpmlist.newsrv	2009-01-08 15:45:09.239815270 +0100
@@ -12,7 +12,6 @@
 audit-libs-1.6.5-9.el5
 audit-libs-python-1.6.5-9.el5
 authconfig-5.3.21-3.el5
-autofs-5.0.1-0.rc2.88
 autofs-5.0.1-0.rc2.88.el5_2.1
 bacula-client-2.0.3-10.el5
 bacula-common-2.0.3-10.el5
@@ -21,12 +20,9 @@
 bc-1.06-21
 beecrypt-4.1.2-10.1.1
 bind-libs-9.3.4-6.0.2.P1.el5_2
-bind-libs-9.3.4-6.P1.el5
 bind-utils-9.3.4-6.0.2.P1.el5_2
-bind-utils-9.3.4-6.P1.el5
 binutils-2.17.50.0.6-6.el5
 bzip2-1.0.3-4.el5_2
-bzip2-libs-1.0.3-3
 bzip2-libs-1.0.3-4.el5_2

I found this a bit strange, these were simply set up and updated via yum
update, the normal way.
Checking the syslog confirms, with events like this :

messages.3:Dec 19 10:08:45 oldsrv yum: Updated: bzip2-libs -
1.0.3-4.el5_2.x86_64

Is this a known issue? Is this even Yum related or RPM related?
In case this is a known issue, is there an easy way to purge the old
versions of said packages?

Any light shed on this issue would be very welcome. I'll check Red Hat
Bugzilla too.

Best Regards
-- 
Denis Braekhus
Team Lead Managed Services
Redpill Linpro AS - Changing the game