I never forget a face, but in your case I'll be glad to make an exception - Groucho Marx
He reported the bug to Microsoft Finland some time ago but so far the outfit hasn't graced him with an answer. He has asked us to alert you to the potential problem.
According to our reader, this is how it works, or rather doesn't work:
Make a private appointment to your calendar.
Go to another computer, use an account that is not yours, and open your calendar from there.
Try to open that private appointment, you won't be able to do that.
Open any other appointment adjacent to the private one.
Click "next" or "previous" in the toolbar of that adjacent appointment.
He reports: "Voila, you'll see the details of that private appointment like it was not a private one!" µ