One sign-up field not included in PDb_List::_setup_iteration list query

I am currently attempting to set up Participants Database to manage what the documentation refers to as ‘two databases’: a listing of face-to-face parenting programs, and a list of online parenting programs. It looks to me like this is quite a doable task in Participants Database owing to its wonderfully flexible and extensible design, which I am really appreciating. It’s really a fantastic tool.

One thing puzzles me. I have a field called ‘age_group’ which appears on my signup form for both program types. The ‘Signup’ checkbox is checked for the field, and I have not written any kind of filter which might conceivably have caused it to be removed from the query that ultimately generates the records available on a page with the [pdb_list] shortcode. For example, I have not applied any kind of pdb-list_query_object filter. A call to Participants_Db::get_field_def(‘age_group’)->stores_data() returns true, yet the field does not show up in my PDb_List::_setup_iteration list query, which currently reads:

SELECT p.id, p.how_is_this_program_delivered, p.town, p.address_1, p.brief_note_to_accompany_listing, p.day_program_runs, p.start_time, p.end_time, p.facilitator_1, p.program_type, p.approved, p.address_2, p.organisation_3, p.email, p.organisation_1, p.publication_status, p.date_last_verified, p.role_of_person_who_handles_enquiries, p.organisation_2, p.facilitator_2, p.person_who_handles_program_enquiries, p.phone_number_for_enquiries, p.state FROM 89E_participants_database p ORDER BY p.date_updated DESC

For now I am working around this problem by running a direct wpdb query to retrieve the age_group data for each record whose details I am displaying using a custom template, but I suspect whatever is causing this problem may yet bite me in other ways (I haven’t yet finished implementing my whole setup).

Can anyone give me any hints as to how to troubleshoot this problem further?