On Outlook 2011 for Mac if someone creates a meeting and includes external invitees (in this case Google recipients). The external user accepts the invite and the originator receives the notification email with the "invite.ics" attachment. The attachment is read and the appointment is updated with the attendees status as normal. However if the Outlook 2011 user the created the meeting actually opens the attachment in the response email it breaks the meeting, basically converts it to an appointment and removes all the invitees.

I am able to reproduce this and it does not happen in Outlook for Windows.

Thank you