I found a rather embarrassing bug in the 2.7-series of the calendar that causes event specific permissions to be ignored when checking which buttons to show in the modal view of an event. Especially people where not shown the “delete” button to delete their own events; instead they need to go to the detail view and delete the event from there.
This is not a security relevant issue (e.g. when people should not be able to edit a certain event, they might wrongly see the “Edit” button, but get an error message when actually trying to edit), but still
Anyway, please update to 2.7.3 to get rid of the issue!