Sadly, errors like this are usually symptoms of organizational problems. Code cleanliness, testing and QA, are all very easy to sweep under the rug, and neglect/abuse organizationally. In the short-term, everything still seems fine. In the long run, problems like these keep snowballing. Once a trend like this starts, the only way to reverse it is via organizational shakeups.

I hope I'm wrong, and that a bug like this happened purely due to dumb luck. But somehow, I'm doubtful.