User blog comment:Wolf Hexskull/TERRIBLE BUG/@comment-70.59.227.121-20120912013621/@comment-1140008-20120912102904

It's extremely rare, but the developers can perform something called a progress reset. What it does is basically erases anything you did in the past week, as if it never happened. If he got Hull Ripper during a time period that was reverted, that's probably what caused it.