Cluster Failback does not work

Hi,
we are running a MS Cluster on two W2K Advanced servers. When I setup a cluster resource to automatically failback at a specified time, this just does not happen. The cluster is working properly, failover works fine.
Does anybody have an ideawhy the failback would not work.?
An example:
Resource A is setup to automatically failback between 20h00 and 22h00. Resource A is failed-over from Node1 to Node2 during the day due to a hardware failure. We fix the hardware problem and expect Resource A to failback to Node1 automatically between 20h00 and 22h00. -> This does not happen. No messages in the event log.

Thanks in advance!