When receiving a MR (even with https://jira.kopano.io/browse/KW-1347 fixed) sometimes the meeting shows up twice in the Outlook calendar.
One of these meetings comes from the server, has properties 0x6B20 & 0x6B21 set. The other one is only created locally, doesn't has the properties as the other one, but 0x6B23 set. That one contains the ID of the MR of the Inbox.
The first one is created by kopano-mr-process and sometimes synced before the MR email is synchronized to Outlook.