[CentOS] yum upgrade on 3.4 and spamassassin

Hello,

I run CentOS 3.4 on 3 machines (i386). Original yum.conf

If I do a yum update: No actions to take

If I do a yum upgrade a machine that has no spamassassin: No actions to take

If I do a yum upgrade on 2 machines that have perl-Mail-SpamAssassin-3.0.1-1 installed (3rd party rpm, more recent than the CentOS/RHEL one):

I will do the following: [update: spamassassin 2.55-3.4.i386] I will install/upgrade these to satisfy the dependencies: [deps: perl-Time-HiRes 1.38-3.i386] Is this ok [y/N]:

Could someone please explain this behavior? Why is yum upgrade trying to upgrade a package that is a newer 3rd party rpm, with a different name?

Thanks, Francois