No one can answer that question. Your original issue is not the norm, so no one can tell you why it happened . Likewise, history is not necessarily an indicator of future actions - just because it happened once that doesn't mean it'll happen again..
Ultimtely, though, even resetting the iPod isn't the end of the world. A minor PITA followed by a re-sync.
Ony a very few users have problems when update. Just makes sure that you backup yuor iPod before updateing and make sure that all yu synced media like apps and music are in your iTunes library sincesynced media are not included in the backup. To update see: