Calendar Invitations
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Until recently, when my other half and I sent each other invitations to appointments (we don't talk any more), they arrived in the Calendar app's appointments box from where you could accept or whatever the appointment. Recently (last several days) we have experienced (in both directions) invitations arriving by E-Mail instead.
This is irritating but the fact that the accept etc buttons in said E-mails do not do anything makes the whole thing a real problem.
Any other victims or thoughts?