[CentOS] Postfix not set top start after upgrade

I noticed that after the lastest yum update on CentOS 5.6 we get Postfix
2.3.3, but the status of the postfix service (chkconfig --list postfix)
changes to off. So after a reboot, it doesn't start automatically. 
I don't recall this ever happening before. Is this by design? A
packaging error?

Thanks,
Micha