Fun little blog entry documenting the life and death of a bug in Microsoft Word for Mac. A nice reminder of how difficult it can be to predict how your shiny new feature will interact with old code, and, more importantly, why it can take so darn long to fix an “obvious” bug. I’d love to see a similar explanation of Apple’s “can’t use capital U in firmware password” bug.

One thing this story doesn’t touch on is the importance of clear, unique error messages. If Word had actually reported “too many open files” instead of “disk full,” the problem might have been fixed a lot sooner. In one of my own favorite debugging stories, our discovery of the message “oh shit: fState != kParseError” led us directly to one line out of 16,000. It wasn’t clear, but it was at least unique.