Mappings from search builder saved with mapping_type_id = NULL

Using the search builder to create a dedicated smart group (or hidden for mailings) creates a mapping and the assiciated mapping fields.
Since the mapping_type_id is NULL it shows up as a deletable empty row in http://dmaster.demo.civicrm.org/civicrm/admin/mapping?reset=1
Deleting it results in a non-working smart group without the ability to modify the mapping fields for the group due to a DB Error:

[info] $Fatal Error Details = Array
(
[callback] => Array
(
[0] => CRM_Core_Error
[1] => handle
)

[code] => -3
[message] => DB Error: constraint violation
[mode] => 16
[debug_info] => INSERT INTO civicrm_mapping_field (mapping_id , name , contact_type , column_number , grouping , operator , value ) VALUES ( 53 , 'group' , 'Contact' , 0 , 1 , '=' , '229' ) [nativecode=1452 ** Cannot add or update a child row: a foreign key constraint fails (`civicrm`.`civicrm_mapping_field`, CONSTRAINT `FK_civicrm_mapping_field_mapping_id` FOREIGN KEY (`mapping_id`) REFERENCES `civicrm_mapping` (`id`))]
[type] => DB_Error
[user_info] => INSERT INTO civicrm_mapping_field (mapping_id , name , contact_type , column_number , grouping , operator , value ) VALUES ( 53 , 'group' , 'Contact' , 0 , 1 , '=' , '229' ) [nativecode=1452 ** Cannot add or update a child row: a foreign key constraint fails (`civicrm`.`civicrm_mapping_field`, CONSTRAINT `FK_civicrm_mapping_field_mapping_id` FOREIGN KEY (`mapping_id`) REFERENCES `civicrm_mapping` (`id`))]
[to_string] => [db_error: message="DB Error: constraint violation" code=-3 mode=callback callback=CRM_Core_Error::handle prefix="" info="INSERT INTO civicrm_mapping_field (mapping_id , name , contact_type , column_number , grouping , operator , value ) VALUES ( 53 , 'group' , 'Contact' , 0 , 1 , '=' , '229' ) [nativecode=1452 ** Cannot add or update a child row: a foreign key constraint fails (`civicrm`.`civicrm_mapping_field`, CONSTRAINT `FK_civicrm_mapping_field_mapping_id` FOREIGN KEY (`mapping_id`) REFERENCES `civicrm_mapping` (`id`))]"]
)