Ask HN: Mistakes from inappropriate use of diagnostic code

I was reading "Fear and Loathing and Windows 8" (http://mobileopportunity.blogspot.com/2012/05/fear-and-loathing-and-windows-8.html) when I came across this statement, "An OS almost always gets faster right before it ships, because the last thing the engineers do is strip out all the diagnostic code they were using to track bugs."

Has anyone seen a situation where stripping out the diagnostic code has caused crashes, because someone's code was using what was supposed to be purely diagnostic code to perform a function?