UPDATE: I think it was joehonest, Markus just confirmed it. I did some searching and found a link to this Ask Audyssey thread where Chris confirmed that Onkyo dropped the polarity check: https://audyssey.zendesk.com/entries/270385-speaker-polarity
So, nezff, the reason you didn't get it with the Onkyo and now get it with the Denon is that Onkyo dropped the feature!
Nice one batpig. I will amend the FAQ to incorporate this news. Thanks.