Why (else) would my Calendar icon have a red badge (with numbers) on it? Supposedly, the red badge that shows up on the Calendar icon in the app switcher (and the Dock, if anyone still uses that) represents invitations that you've not dealt with.  That's a nice theory, but I have no invitations waiting for me to act on, and I still have a red badge with a "3" in it.

I realize that I can disable the badge, but that seems like taking a hammer and smashing the light on the dashboard, instead of figuring out why it is lit up.  

I want to know what (other than invitations waiting) could cause a red badge to show up on the Calendar.app icon.  If this is a bug (e.g. where Calendar is failing update its count of invitations) is there any way to fix it?  Is there any way to reset it?  If it's not a bug, what other entities get counted besides invitations?
I had the same issue, disabled and reenabled the icloud account in calendar preferences and it got rid of the phantom badge