The source of their index.php, and the subsequent discussion on HN. Just imagine someone franticly trying to get into insert mode, and saving on a production server. It stayed like that for a reasonable period before someone noticed.
That doesn't necessarily mean that they don't use source control or build control. The index file linked has tons of production-specific configuration information (database ip/keys), which wouldn't be checked into source control under best practices. That would require manual editing on the server to set up correctly.
http://pastebin.com/raw.php?i=aPQJUh1Q
http://news.ycombinator.com/item?id=2343330