constraint violation when deleting some relationship types

When you attempt to delete a relationship type that is contained in an import mapping, you get a constraint violation:

DB Error: constraint violation

Database Error Code: Cannot delete or update a parent row: a foreign key constraint fails (`oa_civicrm/civicrm_mapping_field`, CONSTRAINT `FK_civicrm_mapping_field_relationship_type_id` FOREIGN KEY (`relationship_type_id`) REFERENCES `civicrm_relationship_type` (`id`)), 1451