I started work on the bug reported in the previous post, by reproducing the structure required in the Potluck test db and trying to confirm what was happening. I couldn't reproduce it at all. So I went back to the original Landscapes local_classes.php file and searched for anything that might be anomalous. What I found was that the two fields in the owner table that linked to the titles as owner and seller had the same field name. That was obviously wrong, and was a good candidate for causing all the issues we'd seen. I fixed the issue in the dev db and tested as thoroughly as I could, without being able to trigger any errors, so I've now asked the field team to test the dev db, and if they can't break anything, we'll port the fix to the live db (and obviously test again there).
If this is fixed, it will free me to implement read-only access as requested by JSR.