Here is a summary of the issues I see. The final listed settings provide a workaround, but confirmation messages are still not being sent to the invitation originator.
TB 3.1.10 Lightning 1.0b2 Provider 0.7.1
enableEmailInvitations=false
Issue: Invitations received at an email id other than the primary email id associated with the google calendar are not seen in TB email.
enableEmailInvitations=true sendEventNotifications=true enableAttendees=true
In lightning calendar properties, assign E-Mail pulldown to the email id to which invitations are being sent
Issue: Invitations are seen in TB email. However, accepting an invitation causes it to be resent to all attendees with me as the originator. (very nasty bug)
enableEmailInvitations=true sendEventNotifications=false enableAttendees=true
In lightning calendar properties, assign E-Mail pulldown to the email id to which invitations are being sent
Issue: Invitations can be seen in TB email, and accepting one correctly adds it to the calendar. However, confirmation responses are not sent to the originator of the invitation.