How to stop birthdays from getting into my calendar?

[cheshirex]

Whenever I edit a contact to add an event date like a birthday, that somehow gets added as a repeating (annual) event in one of my calendars. Just by itself, that's annoying, since I use a third-party app to track such events and don't want them in my calendar. What's doubly annoying here though is that these events do no go into my birthdays calendar -- instead they go into a different calendar which I have shared with my wife, and she complains whenever reminders come up for birthdays for people she doesn't know.

I have an LG G4 running Android 6.0, and also use Business Calendar. I've searched for appropriate settings in the stock Calendar application, in Business Calendar, in Contacts, and even disabled all birthday synchronization in Google+ with no effect.

Any ideas are appreciated...

Thanks!