This is an offshoot of the previous question but what is the toughest bug that you yourself personally found and eliminated? How did it manifest and how did you find it? If the solution was interesting, add that too....
Without thinking overly much on it one memorable bug was when I was working for this medical insurance billing firm in the early 90's. Once a month they had to print invoices and without fail after a few hundred thousand invoices it would crash the system. My team and I looked at the code for a week (it was a non-trivial amount of code) and could find no answers for the crash; it was all just math, no fooling with pointer math or intense system calls (Not that it matters but this was on Win31).....turned out the HP laser printer driver had a memory leak in it which was only revealed when we switched the printing of invoices to a dot-matrix printer (and the crashes went away). Printing single-document jobs of course would reveal no bad behavior but after a lot of prints the system would crash in unexpected ways. Because it was a printer that was designed to print in high volumes, swapping it out for another of a similar type was out of the question. While the finding of the bug wasn't true C++, the nature of the crash made us look hard at our own code thinking the issue was there....
Another more code-oriented bug was one which was plaguing a firm I once worked for that ran a mixed environment (Win31, DOS, OS/2). Symptoms were that occasionally when an OS/2 windowed app was started and then later closed, it would also close/kill some other seemingly random application, even if it was a DOS or Windows app. The problem was a bug in the windowing library (XVT ) that was used where through some brain-dead logic when it created a child window from a parent, it would create the child and then store the ID of the window just created, usually the one with focus. For those who don't see where this is heading if the user started this app and before it finished started any other app in the mixed environment, the parent of the app using Xvt would attach itself so a random child window (whatever had focus under the mistaken idea that since it created the window, the child with forcus was his) and thus, when the parent window/app was closed it would take out the child window it had attached itself to, regardless of the child windows' true parentage. Getting these symptoms reported by non-computer folk muddied the waters even further. That one was the source of a great deal of profanity....
I have more but that was one of the tricker ones to catch.....what is your personal best/worst?
Peace