This touches a lot of chords (oops!) with me - I have this theory (unfettered by any known facts) that there is or was a scale with an "ambiguous" seventh - approximated to by the melodic minor so much loved (ie hated) by struggling pianists in which the seventh is sharpened on the way up, but flattened on the way down. In fact (the theory goes) it should be somewhere between the two in either direction - not easily achieved on a keyboard or fretted instrument) The best example I can think of off the top of my head is "Underneath her apron" ("A fine young girl all in the month of may . . . etc) also used as an alternative tune to "O Joseph being an old man truly". This accounts for the fact that such tunes are difficult to harmonise, and when harmonised sound totally different. In fact the tune sounds totally different when played unharmonised on the piano, which I attribute to the fact that the seventh cannot be ambiguous, exaggerated by the effect of equal temperament and the overtones produced on the piano. But it's all speculative . . .

SJ