Actually, I'm glad this thread came back--a Fuji tech CALLED me on the phone and talked to me for fifteen minutes about the problem! He led me through my whole process, and we figured out that I'd done one particular thing differently from usual--I pre-soaked the film for a minute in tap water. I don't usually do this, but I do when I develop C41, because I like to get the film up to temperature before I pour in the dev. And I had been souping C41 the same week, and so automatically did this to the Neopan.
Anyway, we have a potassium-permanganate-based well water treatment system, and it's possible that the tank had just recycled, and there were traces of the chemical in the water. This doesn't explain why the images themselves weren't flaking off, but it is the only thing I did differently.
Next roll, I won't soak, and I'll see what happens.