Why maintain a deleted image-membership ?

I create a image member at first, then delete it, then create it again with the same parameters. In DB, we can see there are two image-member records between the same image and tenant, one is marked as deleted, the other is not. Is this a correct behavior ?

I'm wondering why can't we use only one record to maintain the member-ship between image and tenant, just update the "deleted" column when the same image-tenant pair membership is created or deleted ? Is there any reason for maintain the deleted memberships in DB ? This is related to : https://review.openstack.org/#/c/190895/