I'm running CiviCRM 5.10.4 on top of Drupal 7.63 on Debian, with localisation.
My contacts have UK-style postcodes with the first half (e.g. "M19") stored in "Postal Code" and the second (e.g. "3JD") in "Post Code Suffix".
I am trying to get a list of my members, with full postcode data, as a CSV. I generate the built-in "Membership Report (Detail)" which is at
/civicrm/report/instance/20 for my instance. I then add the "Postal Code" and "Post Code Suffix" columns (among other address ones). The data displayed in "Post Code Suffix" is identical to that in "Postal Code", e.g. they are both "M19". This is also the case in an exported CSV of the report.
The correct data is in the database - clicking on any "Contact Name" from the report takes me to the individual "View Contact" screen, where the Post Code & Suffix are correct (e.g. "M19" "3JD").
Any idea what's going on here or how I can fix this?