Hi,
These enigmatic and mysterious phenomenon it's very strange because the glass frosting are made by means of any chemical attack process, normally with fluorhyidric acid. So, the "frosting" cannot be "peeled" from the glass surface, because is the glass itself that are microscopically corroded by acid, unless that your bulb not were a true frosted one, but internally coated by any kind of ultrafine and traslucent dust layer that appears more as a frosted surface than a traditional opalescent milky coating. In such case, the coating could be gradually falling of the glass surface leaving the bulb in a clear appearance. It could be originated along the lifetime by the normal heating of the lamp.
Here in Europe these kind of "fake" frosted bulbs are becoming very common today, especially those manufactured by Philips Europe and sold within moulded plastic blisters instead in cardboard boxes.
Please, see carefully your bulb and check for any trace of free dust "dancing around" inside the lamp.
Best regards, merry Christmas and a happy new year for all.
M. Gonz?lez.