OK, since we're at counterpoles on this - and I concede your expertise in this area, TC - I will say that my comments
were based on a 2009 version of Hugin which would balk at any moderate difference in sky tone (mainly sky tones).

I notice too that you say "usually gives a good result". I never used the method you describe so it would be interesting to try next time
I do this in such circumstances. Now I have the latest version of Hugin. (I couldn't run it on my other machine.)

Am.