[CentOS] swap labeling annoyance

I just upgraded a blade server via rsync from another server. Rebuilt the
initrd. It boots fine... except that it won't turn on the swap partition.
Several times, I've made sure swap was off, then mkswap -L SWAP-sda3
/dev/sda3, but when I do swapon -L SWAP-sda3, it complains it can't find
the device for the label.

The only thing I find while googling, other than redoing what I've done
several times now, is an old bug from CentOS 4, 0001399, which affected
*only* blade enclosures: the reporter says that all of his IBM blades were
affected (this isn't an IBM). His workaround was to make an ext2 fs, label
it, and turn that into swap.

Has anyone seen this recently, with 6.2?

       mark