Shared Events dragged from an Object Editor show as an "Event ref" on the clipboard and include a Role. You can drag an "Event" to a CardView Person or Family, but that is not possible with an "Event ref".
Note that when dragging an "Event ref" to a Person or Family Editor, it does not pop the standard event editor with an "Unknown" role like . Instead, it simply clones the Role when adding the Event to the Person or Family.