Thinking about this - I bet it's a Leap Year issue (some dumbass set a "days in the year" upper bound at 365 days) and since it was first released in 2006, this would be the first time it has occurred.
It's odd that it's only affecting the 30GB version though. I would expect the software to be the same unless one version was just manufactured with different software.
i wonder if the leap second could be a catalyst, especially if the zune 'year' is really just a collection of seconds sectioned into 'days' meaning december 31st is an anomaly that has been encoded with 1 extra second.
