In the installer environment, /dev/md/ does not exist prior to anaconda attempting to run mdadm -I. Because mdadm wants to store a map file in /dev/md/, and without it fails to assemble devices properly in incremental mode, anaconda is having fits. So, I patched mdadm to store its file in /dev/.mdadm.map instead (this is guaranteed to be writable on first call to mdadm -I during normal bootup, where as /var/run/mdadm.map was not, hence the original move to /dev/md/mdadm.map, but since /dev/md isn't always available either, use /dev/.mdadm.map). I've installed the new mdadm and verified that it does indeed use this new location to store its incremental assembly map file, and that incremental assembly worked as expected.

Build n-v-r is mdadm-3.0-0.devel3.6.fc11, requesting party from Anaconda team is dlehman.