I don't even know what to make of this. Reader DreamingHawk asked Black Forest Games about their upcoming Giana Sisters patch, which should tackle the lack of GamePad audio when playing the game in Off-TV mode. According to Black Forest Games, this actually isn't a bug.

Hi, currently we don't have a release date nor a projected date-frame for NA. The missing sound is not a bug, it is a known behavior which does not violate the technical guidelines of the WiiU.

That's an awfully strange response, don't you think? Clearly it ruins part of the experience when playing on GamePad alone. Why not work to fix it right away?