We have a calendar in application root, and a site role which was granted event create/edit permission to the calendar application itself
We can add new calendar events via a user in the role but any tags are being ignored and not saved as expected
After some more investigation we had to also grant event create/edit permission to the role at the group level for calendar events and now tags are saved as expected
It seems that the permission check on adding/updating tags is not taking into account the permissions at the application level and only checking at the group level.