I don't think it's too disrespectful to summarize this article with a TL:DR.<p>They were using RCS to do version control of some unknown files in their language. This caused a bunch of IO to happen intermittently when they were doing relatively simple operations.<p>This looks like the most common cause of "wow it sure is hard to figure out what causes this occasional problem": "we didn't know all of the stuff our code was doing."