I worked on a code base that ran on a variety of Unixes. One customer complained about file corruption from our software. Turns out that their Unix setup was.

I worked on a code base that ran on a variety of Unixes. One customer complained about file corruption from our software. Turns out that their Unix setup was... rather unique. Spawned programs were not given a stderr file handle! If you wrote to stderr, it scribbled on whatever file was open on file handle 2. We, uh, reasoned with the other side - we told them to fix their stupid broken setup.