[CentOS-virt] xenbr0 isn't created anymore

Somehow I managed to disable the creation of xenbr0 on boot-up of the host system. CentOS 5 with standard CentOS Xen. I changed all Xen VMs to use xenbr0 instead of virbr0 and disabled virtlibd. Works fine. But when I later restarted the machine I found that all networking for guests had gone. On inspection there's no xenbr0 created anymore. I can get it up by stopping network (or eth0) and then running /etc/xen/scripts/network-bridge start xend-config.sxp still has (network-script network-bridge), logging shows no problems. It seems that the network-bridge script simply doesn't run, but why? I can't see any init script or so that might run it, so I assume it's xend doing that, but there's no error in any log.

Kai