On this URL: http://wiki.centos.org/Repositories it says:
Note: You should seriously consider using the Priorities (or ProtectBase) yum plugin if you are going to use a 3rd Party Repository. (The Priorities and ProtectBase plugins both prevent 3rd party repos replacing base packages, but Priorities is much more flexible and therefore the recommended plugin.)
Consider removing ProtectBase and installing Priorities
Hey, Why should I remove ProtectBase ? Whithout removing ProtectBase, Is it NOT proper to install Priorities?