I am looking for an example of how to use the new DataServiceState Save and Restore methods in a WP7 application in order to tombstone a datacontext - I cannot find any examples and the approach I used resulted in an exception

this saves the data context correctly

PhoneApplicationService.Current.State["DataContext"] = DataServiceState.Save(this.Model.Entities);

this attempts to restore it after the app is re-activated

var dc = (PhoneApplicationService.Current.State["DataContext"] as DataServiceState).Restore();

but throws an exception

An item could not be added to the collection. When items in a DataServiceCollection are tracked by the DataServiceContext, new items cannot be added before items have been loaded into the collection.

This is the same exception I get if I try to reload a datacontext that I stored "directly" (without using the DataServiceState.Save method) in the PhoneApplicationService.Current.State. I cannot find any offical documentation on the new ODATA v2 DataServiceState class or examples.

thanks Michael