API v2 outbox query is missing the recipients field

When trying to list a user's sent Private Messages using API v2, I can't explicitly include "recipients" as a field in the query. I need to query "*" and then it does become available for use.

E.g. instead of querying

SELECT id,recipients FROM outbox_messages WHERE ..

I'm forced to SELECT * FROM outbox_messages WHERE ..

If I SELECT *, I can <#list recipients and query recipients.items.

User error, bug or unfinished feature?