[Users] Nested kvms

Hi list! I've been playing lately with nested VMs in a configuration where I have a VM for the ovirt-engine and another to be used as a host (both created with virt-manager). After adding the virtualized host to the engine, I could start VMs but their boot process was always hanging/kernel panicking. The cpu type I had set for the virtualized host was Sandy bridge. After some trial and error, I changed the cpu type of the virtualized host to Conroe (as well as the cluster cpu type) and suddenly I can run VMs well through installation and usage without any kind of trouble. My question is... Any similar experiences? Or is it possible that in the meantime some yum update to qemu-kvm fooled me? Best, Toni