The connection between the ciscoworks GUI and the DFM repository is not 'optimal', or something like that. It's complicated.
What could cause the behavior you mention however, is either someone rediscovering devices that are still in learning state, or the presence of multiple active rediscovery schedules.
You may even delete all schedules excepts the default redisovery schedule which you can/should suspend. If the problem then stays away you know what caused it.
At this stage any device that really changes must be rediscoverd in DFM manually.
I think Admin -> Fault takes you to a page showing the schedule, if not lookup 'fault rediscovery schedule' in the help.
Cheers,
Michel