I have the same issue. I purchased the Character Add-On pack on Dec 28 and all the cards are about 1mm shorter than the cards in the base set. This makes them harder to shuffle as the shorter cards make groups of cards stick together. Also, many of the card backs are lighter in color than the base set. I picked up Adventure Packs 2 and 3 at the same time, but the cards in those sets are the same size as the base set. Any chance a Paizo rep could respond? If it's a printing error, I'd like to send the smaller cards back and get a replacement set.
Recently purchased(yesterday) the Base set and Character addons. All of the cards in the character addon set are roughly 1mm smaller in length than those of the base set (same width). Did I get a weird batch or are they all like this? Are the additional adventure packs the same size as the base set or the character addons? Just curious.
Looking forward to playing it this coming week with friends.