Why do people think this is the right approach?  So we have a flaw in System A, the logic is not right.  Let’s change the way System B works to mask the flaw in System A.  Sounds like an excellent plan, right?

WRONG!

Talk to the manager of System A, and you will hear the blame thrown everywhere but where it should lie.  “It was correct as written”, “It was signed off as correct”, blah blah blah.  The problem is that the wrong people signed off on his System, but not everyone.  If the System has had the same issue since it was created, and now it is considered a bug, it was a bug when it was created.

Sad thing is, this happens all the time.  You continue to put a band-aid on an issue, and add another band-aid until it explodes.  Why not just save all that time and fix the initial issue!