pygrub uses a cached and eventually outdated grub.conf, kernel, and initrd in Red Hat Enterprise Linux 5

Issue

• After performing a kernel upgrade in a domU and rebooting, pygrub uses a cached copy of the grub.conf and therefore boots using an old kernel/initrd.
• xen boot menu does not match /boot/grub/grub.conf.
• We have a xen pv that was recently re-kickstarted.  I am quite puzzled why the machine does not boot the kernel set as the default in /boot/grub/grub.conf.  It should be booting the 2.6.18-128.1.14.el5xen kernel, but it always boots 2.6.18-128.el5xen.