Exchange calendar sending many invitations

I'm on Yosemite 10.10.2 and I'm using Mail and Calendar with an Office 365 Exchange account.

Lately, people (outside my organization) have been telling me that they receive many invitations for events which I have created in Calendar on my Mac and invited them to.

1. I use Calendar to create an Exchange calendar event.
2. I add some as an invitee.
3. I save the event and the user accepts the invite.
4. Some point prior to the event, the user starts receiving invitations for the same event again, as if I were editing them and resending the invitation, but I'm not doing anything at all.

Anyone else experiencing this?

 

Why was this moved to Mac Applications? This is an issue with Calendar.app, part of OS X.