The photo tells the story. The back of the headstock looks the same, and there is a little of this on sides at the upper bout, and a spot on the back. Based on Frank's warning about using polishes on old finish in the "Cleaning" article on Frets.com, I am guessing someone tried to do just that (yes, it came to me this way).
I have tried water, mild detergent, naptha, and denatured alcohol. In each instance, the white stuff completely disappears so long as the surface is wet. As soon as the surface dries, the white stuff comes back unchanged.
So, I tried an experiment. I had used Dr. Duck's Ax Wax (recommended by LMI) as the last step when I built my StewMac 000. I rubbed a little on the back of the headstock and the white stuff disappeared. I gave it a good buffing and let it sit for 30 mins. and it still looks great -- rich color, lustrous glow.
But, have I solved the problem or only postponed it? And, is there a "real" solution?