[libvirt] domain.info() sometimes returns state zero for running machines

I'm using Xen-3.2-1 on Debian 5.0.1-lenny and retrieve information about running domains using domain.info()[0] The domain object is retrieved via connection.lookupByUUIDString(...) and stored as a variable called "domain". Usually the running domains have the state 1 (VIR_DOMAIN_RUNNING) or 2 (VIR_DOMAIN_BLOCKED), but sometimes it happens that 0 (VIR_DOMAIN_NOSTATE) is returned. Why does that happen? I don't think it is an error because then it would've raised an exception... Regards Andreas