One Stamp?

This is our Christmas card for 2008. We ordered them through Costco and when we picked them up, I was surprised at how big they were this year. I told the person at the camera counter and she assured me the postage was "still one stamp".
So, a couple of days later, Rick and I got all the letters addressed and stamped and I headed to the post office. I had a package to send, so I waited through a line and up to the counter. I asked the postal worker to check the cards I was sending out of the country, to make sure I had enough postage. She then asked about the other stack. I told her they were "domestic". She then gave me my total for the "foreign" mail and then told me the cards I was mailing were too big for just one stamp. She checked them in a little cut-out thing and told me each card I was mailing domestially would cost an additional $0.41(not to mention the additional $7.00 I spent on the "foreign" cards). What?? Eighty three cents PER card? You have got to be kidding me. I explained to her I was assured they were only one stamp and she again checked the size and said there is no way. I was ticked. We had about 48 cards to send.
When I got home, I called Costco Corporate and explained the situation. I was told to call the store directly where we ordered the cards. So, I did. I talked to a really nice person in their photo department and she told me they were worried about the size as well, but they had been told the postage would remain the same. She told me to bring in my receipt from the post office and they would reimburse me the additional postage. I was so thankful.
Today we received to cards from other friends, that they had ordered through Costco. They had only one stamp on them ($.43) and they made it just fine. Maybe our post office is just strict or other post offices just didn't care with the holiday rush.