Unable to create new membership type without setting a relationship

I ge the following after creating a new membership type and not specifying a relationship type. I can't view the membership types page after that and have to delete the new type in the DB to continue.

It seems to be setting relationship_type_id to 'Array' in civicrm_membership_types, but leaving relationship_direction null. If I switch relationship_type_id to null in the DB row, then the page loads and everything's fine again.

Database Error Code: Unknown column 'label_' in 'field list', 1054
Additional Details:

Array
(
[callback] => Array
(
[0] => CRM_Core_Error
[1] => handle
)

[code] => -19
[message] => DB Error: no such field
[mode] => 16
[debug_info] => SELECT id, label_
FROM civicrm_relationship_type

WHERE ( civicrm_relationship_type.id = 0 )

[nativecode=1054 ** Unknown column 'label_' in 'field list']
[type] => DB_Error
[user_info] => SELECT id, label_
FROM civicrm_relationship_type

WHERE ( civicrm_relationship_type.id = 0 )

[nativecode=1054 ** Unknown column 'label_' in 'field list']
[to_string] => [db_error: message="DB Error: no such field" code=-19 mode=callback callback=CRM_Core_Error::handle prefix="" info="SELECT id, label_
FROM civicrm_relationship_type

WHERE ( civicrm_relationship_type.id = 0 )

[nativecode=1054 ** Unknown column 'label_' in 'field list']"]
)