Issue with meetings and external attendees

Hi,
I have encountered an issue with meetings that contain external attendees 

I setup a meeting with internal attendees set as resources (because the attendees should not see each other).
These attendees can forward the meeting to external addresses, which adds the new attendees to the optional list 

In this type of meeting I encounter 2 different behaviors:

- When adding new attendee as a resrouce by the meeting organizer (internal address) an invitation email is sent only to the new attendee

- When removing a resource attendee from the meeting (internal address) a cancellation email is sent to the removed attendee plus an update email to all other attendees

The full update is sent only when external email attendees appear in the meeting

I want to remove the update email during cancellation

I use exchange 2010 sp1 ru3


Any ideas?

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Assaf