Answer
On IFS Application update levels roughly between 7 and 14, an LOV built against a Reference-type custom field shows, by design at that time, extra duplicate-looking columns tied to the underlying reference custom field's own stored database values, even though those columns aren't meaningful for users to see day-to-day. To hide them: RMB on the column headers within the LOV window itself and choose Properties, go to the Table tab, untick the specific unwanted duplicate columns, and Apply/OK. This per-user fix can be captured into a Base Profile and assigned to affected users to apply it consistently across everyone hitting the same issue. This specific display quirk was corrected starting from Update 15 onward, so upgrading to a later update level, or requesting the underlying bug fix via a support case if staying on an earlier update, removes the need for this workaround entirely.