From the recent EC appeal in the Continued Zeroing (DS350) case:
First, if the Panel Report is construed as finding that a panel can invoke "cogent reasons" for departing from previous Appellate Body findings on the same issue of legal interpretation (paragraphs 7.180 and 7.182 of the Panel Report), then the European Communities requests the Appellate Body to modify or reverse those findings and complete the analysis, for all the reasons set out by the Appellate Body in its report in US – Stainless Steel from Mexico. The European Communities considers that a panel may invoke "cogent reasons" in order to depart from previous panel findings; but only the Appellate Body can invoke "cogent reasons" in order to depart from previous Appellate Body findings. (emphasis added)
I'd love to hear what the Appellate Body has to say on this point. Unfortunately, it was part of a "conditional appeal," and it's rare that the Appellate Body rules on those. My guess is they will not be eager to address it here.