Dave
I haven't experienced that particular issue, as it seems very odd that the dashboard will change state when there are no alarms to make it do so.
I've suffered the opposite in the past with alarms being generated but the dashboard(s) not updating with these new alarms. It turned out to be a bug and was fixed a while back.
When the issue does occur, when you double click the little coloured bar on the dashboard status bar is there anything shown in there as far as alarms go?
Is it a particular dashboard or component on the dashboard?
Also whats the state within the dashboard_server of that dashboard when the proble happens?
Justin