The kernel-PAE-2.6.18-53* packages (and presumably earlier) have a misleading description which READS: This package includes a version of the Linux kernel with support for up to 64GB of high memory. It requires a CPU with Physical Address Extensions (PAE). Except that since this is a 3/1 split kernel we only *support* up to 16 GB of RAM, even though 64GB is addressable; see http://www.redhat.com/rhel/compare/ (especially "Maximum memory: x86" and note 6). Package description should be reworded to reflect this; this is causing confusion internally.
Ok, I'll assign this to myself so I don't forget.
I added this change under another bugzilla, so it should be included in the 5.3 kernel.