This happened to me as well, though in a much shorter amount of time. The coating seemed to soften when in contact with ink. As the coating softened the nib creep got worse, which softened the coating more. Eventually I peeled most of it off the top and now there is no nib creep. I emailed someone at Platinum saying that I was worried that pieces of the coating would clog the nib and they responded that the coating would dissolve in the ink. Which would also explain why it peeled in the first place.
I certainly hope that Platinum develops a method by which this flaking may be remedied. The Preppys truly are great, inexpensive pens, and the colored coating is a great part of the draw to them.