Update to kernel-2.6.32-504.12.2, Grub not updating

I'm having a problem; when i'm updating to the kernel-2.6.32-504.12.2.el6.x86_64 from 32-431 the yum update looks fine. The grub doesn't get updated allowing the system to boot to 504. I've never had a system do this before, what causes this? It does install the kernel image into /boot but grub.conf doesn't get updated. What is the proper way to fix this?