Hallelujah!

> The code to perform raid autodetection is added to the initrd *iff* raid
> sets are detected when mkinitrd is run (ie at kernel install/upgrade
> time).

Indeed, rerunning mkinitrd provides three new modules in the new initrd:
lvm-mod.o, raid5.o, and xor.o.

<slaps myself on forehead>

Thanks very much,
Dan W.