(And on-list again, please use the list for issues like this, others can learn from it, or help)
Hmm. No, I'll run a few tests of my own sometime next week. Unfortunately, debugging %pre is a pain. You actually can't, in text-only mode, as you can't swap out to the console / logs using ALT +f2 / ALT+f3. You'll have to use virt-manager to get to those screens, I guess. Maybe someone has a better idea. If you add that log_ks_pre snippet I just posted to the top of the %pre section, you might have some useful information during that stage under /tmp.
Did this happen for you using the old one as well? (I'd guess so, as the error doesn't indicate LVM).
For info this seems to now be working fine on 1.6.2
thanks