Scheduling and managing events using Outlook.com calendar
@Karla
Like Dansercoer said, the problem is when both Facebook and Outlook contain birthdays.
If no Outlook record exists, the Facebook birthday (if existent) is shown.
If no Facebook birthday exists, the Outlook birthday (if existent) is shown.
This error only applies to "linked" profiles.
As soon as the profiles are "unlinked" and the calendar is resynced, the birthdays reappear.
As Dansercoer stated, deleting the outlook birthdates is not an option because the Facebook profile can be altered by the owner without our knowledge.
Also unlinking the profiles results in our contact list being cluttered with several same name entries.
Also, not an option.
@Karla, I did some more testing. It appears that when a Skype profile is linked then the birthday is lost. If I unlink the Skype, but leave Outlook and Facebook linked, the birthday reappears after refreshing the calendar.