I have a site with (Joomla) authors user group and I've created a separate user group 'organizations'. This user group has 'registered' as a parent. Authors are allowed to submit new articles, but shouldn't have access to adding or editing events. Organizations are allowed to add events, but don't have access to articles.
This works fine, except in the case a user is assigned to both user groups. We have two users in our team who write articles, but also organise events. So they are assigned to both user groups. These users do have access to menu items assigned to either one of the groups. But it seems JEvents only looks at one of the access rights, namely the one of the author group (which has a lower id). So the user might see a menu item for adding events, but if they click on it, they get an error they have no rights to create an event.
I could only solve this by giving the authors event editing rights too, but I have go give them access right to each category too. And even though the authors won't see the Add event menu item, they will see the option below the calendar.