Scheduling and managing events using Outlook.com calendar
This bug is ridiculous. And more ridiculous MS has not fixed it. Here's what I've found:
I discovered if I go to the contact and remove the Facebook or Skype link, it splits the contact into two contacts and it then appears on the calendar. However then you have duplicate contacts and Manage > Cleanup Contacts will merge them back together and the birthdate will disappear from the calendar again.
I then went and removed all linked accounts. The Michele contact in question still appeared but only for Skype. And once again, despite there being a birthdate specified in the account, she doesn't appear on the birthday calendar. And if I recreate her, then I have duplicate contents, and then if I merge via the cleanup, she's not on the birthday calendar anymore. Probably only way would be to either live with the duplicate (not) or delete her from Skype contacts if there is no way to prevent outlook.com from reading my skype contacts.
Very frustrating.
This thread regarding the Skype integration may be related to this issue.