PidLidAllAttendeesString contains unchecked resources from SchedulingAssistant in Exchange 2013

We are impersonating rooms calender to find all appointments and then we book mapped resources in our own system. Now to access the resources that organizer has choosen while creating a meeting we refer to PIDLIDAllAttendeeString. Appointment.Resources is null in this case since organizer created this appointment and from Rooms calender we cannot access this property. Even EWS editor returns resources as Blank for appointments.

                 Object allAttendees = null;
                ExtendedPropertyDefinition prop = new ExtendedPropertyDefinition(DefaultExtendedPropertySet.Appointment, 0x8238, MapiPropertyType.String);
                appointment.TryGetProperty(prop, out allAttendees);

Now we are getting a strange behaviour. Lets say organizer added Room1 from SchedulingAssistance. Unchecked send meeting to this attendee checkbox and added Room2 as well. Room1 calender will get booked but room2 calender won't get booked.

While reading this property we get Room1,Room2 and based on this we get unexpected behaviour in our system. IS this by design?

Are there any other extended property that can provide this information?

Thanks and Regards

Rohit