Scheduler Not Updating When Filtering With No Data Returned

I have a Scheduler bound to an ObjectDataSource that I want to filter using a dropdown list of Categories.  I have a ControlParameter as a SelectParameter on the ObjectDataSource tied to this dropdown.  My filtering works fine if I select an Category that has appointments associated with it and actually returns rows.  However, if I select a Category that does not have any appointments associated with it and returns no rows, the Scheduler never updates and continues to show the previous list of appointments instead of showing no appointments.  Any idea on why the Scheduler won't refresh and properly show no appointments in this situation?