I attributed it to inconsistent state in the database, due to old buggy code, so I wrote those two integrity checking pages.
But, that didn't do it... I still found cases where things worked here but not on the public site.
I traced it to a difference in behavior between the DBI and/or MySQL version I have at home versus there. In all fairness, the behavior change was on a weird corner case (essentially a FB bug: I wasn't trying to rely on the weird results), so it doesn't really matter.... I fixed the bug, and now picpix.com works like it should.
Test away! (but clean your data first with the tools linked off the management page)