New to Notes 8 was the ability to view unprocessed Calendar invites in your Calendar. These invites will show up with a grey background and are great to remind you about possible meetings that you have yet to accept or decline. To enable this feature go to the client Preferences-->Calendar and To Do-->Display-->Views. Enable Display new (unprocessed) notices.
Once this is enabled all new unprocessed Calendar invites will be displayed on the Calendar. Old Calendar invites will not show up because this feature requires the field CalendarDateTime. This field is processed by the router on delivery when the router recognizes this feature is turned on for the user. In the same mannor. If this feature is turned off, they current unprocessed Calendar invites will still display because the field CalendarDateTime is still present in the document.
This is a great feature for users that receive large amounts of email and many calendar invites in a day. The feature helps the user identify potential missed Calendar invites.
Clients prior to 8.5.3 and 8.5.2FP3 could see a problem with this feature that are running in a clustered environment or have server replicas of their mail file across different servers. There is a technical document that once available will be posted here to detail the problem and how to correct.