Comment 1 for bug 262475

This bug has existed since 1.1 (when the overhaul took place), maybe longer. It's extremely rare as it requires that you have a table without primary key AND that they be linked either by name or FK to a table that *does* have a primary key AND that you try to save a new object or change the key for an existing one (you could still update existing so long as you didn't change the primary key).