This is less uncommon than people like to admit. I've seen, and in some cased directly involved with, code written by an inexperienced (giving benefit of doubt here) developer whose position was replaced twice over, that runs critical systems on big-money (but not life-threatening) equipment and business systems. No documentation, no tests, even one that relies on a known platform bug to never be fixed (not kidding). Nobody knows how it works, and there is no time go go through it and clean it up (business decision).

I've even stated in writing on one system that I refuse to receive "emergency" calls on holidays, weekends, or nights to fix a particular system if it ever goes down at that time. Management refusal to plan ahead or heed warnings does not constitute an emergency on my part.