Last month Apple started a replacement program for for the first-generation iPod nano due to continuing issues with overheating related to defective batteries from one of Apples suppliers. Now Macrumors reported that some of their readers did receive their replacement but it turns out to be a 6G iPod Nano instead of a 1G iPod Nano. It looks like Apple may have run out of refurbished first-generation iPod nano units and and may now be shipping out current-generation units as replacements.

Several users have reported over the past few days that they have received emails acknowledging shipment of their replacement devices and checking the serial numbers of the replacement devices on Apples support site has shown them to be sixth-generation models. The sixth-generation iPod nano was originally released in September 2010, and while the line received a price drop and software update a few months ago, Apple still considers the current iPod nano to be a sixth-generation model.

Source [macrumors]