Are you trying to customize these buttons by working in the RoboHelp Output Setup pod? If so, you need to abandon that. It's a horrible way to do it. Instead, use that button in the Responsive HTML 5 recipe card labeled "Customize Selected Layout" and work through the dialog that presents.
If you are already trying this by using the dialog and way I mentioned, I'm at a bit of a loss as to what to tell you. Other than to suggest you report it to Adobe as a bug.