Unable to add events to shared calendar

I want to have a shared calendar between my wife and I so we can both see what social events we have planned.

My wife created a "Social" iCloud calendar using Calendar 6.0 on Mac. She then shared it with my Apple ID, giving me "View and Edit" privledges. I received the notifications without incident, and accepted the invitation. On the Calendar 6.0 app on Mac, and on my iDevices, the shared calendar now appears and so do the events.

Unfortunately I seem to be unable to add events to this shared calendar using the normal interface. When I try to create a new event for this Social calendar, Social does not appear in the list of calendars I can select. When I edit an event that is already in the calendar, the changes propagate to the other devices and to my wife, but when I look what calendar appears to be selected when I Get Info on that event, it says the wrong calendar (a On My Mac calendar that I do not use). Strangely, I can add an event to the social calendar by creating it on a different calendar, then dragging and dropping the new event onto "Social" in the sidebar list of calendars.

The fact that that Social does not show in my list of calendars on my Get Info or right click list is clearly not the intended functionality. The workaround is inadequate because it means I cannot add an event to the Social calendar on my iPhone.

Is this a bug or have I messed up somewhere? How can I fix it? I have already tried unsharing and resharing the calendar, and also deleting the calendar and trying again, both to no avail.

Thanks in advance, I appreciate the help.