Comment 6 for bug 285156

There's no packages for 2.6.26 in the repos anymore, so I built myself some kernel packages from the 2.6.26-5.17 sources, which is listed as the most recent pre-2.6.27 source package in launchpad.

Rebooted, and my array is happily syncing, so it definitely seems to be a problem with 2.6.27.