To me it's the same class of error which is convincing humans and other automated tests that your code is OK when it isn't.

I dealt with a bug that only appeared in release builds, and never in debug. The offending code looked roughly like this:

  if (blah)
    #ifdef DEBUG
    baz();
    #endif
  bar();

The systemic problem was it was a project created by interns, and they'd review each others code. By the time the bug got to me the interns had left and a Sr Dev had spent a day looking for the bug. It took me an hour to find it. In isolation its easy to see but in the mess of all the other code, you really have to look for these things.