Although Red Hat replaced OpenOffice by LibreOffice in RHEL6.3,

It seems that when you keep up with the latest updates in SL you ALREADY have OpenOffice replaced by LibreOffice, even when SL6.3 has not been released.

This is done automatically when you have yum-update active or manually when you "yum update".

If you want to disable automatic updates, you need to remove the package "yum-autoupdate".
Do this as root by giving the following command: yum remove yum-autoupdate.

More details on issues caused by this switch can be followed here.