I have the same problem, different brand, and it's done this since we bought it two years ago. We considered bolting it to the floor but it'd tear up the hard wood floor. W thought about strapping it like they do to keep dressers from falling on children but the wall behind is an old fireplace and there's no good way to anchor it in place. This is no answer but I figured you should know you're not alone with this issue.
Kevin W, June 2015