Maybe I'm just a terrible programmer, but I think the author may be a little over emphasizing the seriousness of the bug. To me, this is one of those throw away issues that you keep in the back of your mind. Unless I'm coding something that is extremely datacentric and critical in that sense. But it's not like its on one of my "top 20 must run tests" or anything. It's always one of those issues I ignore or assume is…
Such mistakes were excusable in the 90s. They're the sign of an amateur programmer today.