If you let your domain expire the DNS system that the internet works on will drop the link between the name and Bravenet. Once you renew it is treated as a new domain and there will be a delay as it propagates across the internet. Different ISPs will refresh their DNS servers on different frequencies, some do it several times an hour, others once every few days!
It isn't a Bravenet issue, the internet just works that way. Ideally you should renew your domain between one and two weeks before expiry to ensure that the update is propagated before the the expiry date.