Persistant software bugs

As this item makes clear, debugging software is challenging:

... OpenBSD developer Marc Balmer has just closed the book on a 25-year-old flaw affecting BSD file systems. He found it when an OpenBSD user emailed him about SAMBA crashing, which he then traced to a workaround SAMBA used to function correctly on BSD systems, which he THEN traced back to a flaw that existed since August of 1983. This bug is in every single BSD system since then, including Mac OS X. The code itself was a very trivial fix, which makes it all the crazier that it took 25 years to do so.