EWS: MyResponseType is 3 [Accept] after room resource declines meeting invitation

We have an application that receives EWS push notifications.  One use case that our customer requires is being able to do the following:

1. create a meeting and invite a room resource
2. the room resource accepts the invitation
3. later, go directly into the room resource calendar and decline the invitation

We do receive an event notification from Exchange when this happens, and we are able to retrieve the Appointment item using Item.Bind.  Once we have the Appointment item, we can check the MyResponseType to see if the room resource declined.

The problem is that we are seeing different behavior depending on whether step 3 above is performed in OWA or the Outlook client.  If the decline is performed in OWA, the MyResponseType property is 4 {Decline} as we expect it to be; but if the decline is performed in Outlook, MyResponseType is 3 {Accept}!  Is this a known issue in EWS, or are we doing something wrong?

Thanks for your help.

John