This is REALLY an obsession I cannot overcome. I will hum and whistle this for days on end.
From www.maurice-ravel.net comes the following quote....
Of the solo part, Marguerite Long later recalled: "It is a difficult work especially in respect of the second movement where one has no respite. I told Ravel one day how anxious I was, after all the fantasy and brilliant orchestration of the first part, to be able to maintain the cantabile of the melody of the piano alone during such a long slow flowing phrase... 'That flowing phrase!' Ravel cried. 'How I worked over it bar by bar! It nearly killed me!'"
(Long, [1973] pp.39-45), Marguerite. Au piano avec Maurice Ravel. Paris, 1971. [English trans.: At the piano with Ravel; ed. by Pierre Laumonier; trans. by Olive Senior-Ellis. London, Dent, 1973.