How to disable unwanted alerts from shared iCloud calendars

We've got shared iCloud calendars setup and working fine, except we get alerts on all our devices for every single change on any shared calendar, to the point that it's obnoxious, and is not something we want. Why is it on by default? We've turned it off on our iPhones, but haven't been successful on our Macs:

Calendar app > list of calendars > Shared Calendar Name > Get Info > "Ignore alerts" is checked, yet alerts still happen.

Calendar app > Preferences > Alerts > "Show shared calendar messages in Notification Center" is unchecked, and this at least does what it says, but alerts still show in Calendar and on the app icon.

Does anyone know how to actually turn this off?