This is one of my favorite bugs of all time: Ubuntu bug #248619, where OpenOffice.org won’t print to Brother printers on Tuesdays (but works on other days of the week).

Read some of the duplicate reports to follow the analysis and developer/user cooperation which isolated the bug.

It’s a great example of a Bohrbug, where the circumstances which trigger the problem can be very difficult to isolate. It’s likely that many such bugs exist in Ubuntu and other software today, but have not yet been isolated, as bug 248619 has been.

We’ve all observed a complex software stack misbehaving in ways we would never expect. It’s just as confusing when things suddenly start working again, for no apparent reason. We start to doubt our senses, or the person who is reporting their observations.

In The Psychology of Computer Programming (chapter 5), Jerry Weinberg presents a case where two identical systems, physically isolated from each other but running the same software, exhibited precisely the same error at the same time. This obviously pointed to a software bug, but after two weeks of searching, the problem could not be replicated and the root cause was not found. The team gave up on finding it, and the system went into production, only to have the bug recur and cause a serious operational outage.

Bugs which occur very rarely may not always be worth investigating, but they are real, and can be explained. When it really matters, we should remember not to disregard them.