Well this is how it played out. While in Japan I made the pilgrimage to Yodobashi Camera and picked up, among other things, a box of 10x12 Fuji Rembrandt paper (100 sheets). Exiting the country, I had the paper (and film) hand checked. Everything was going ok until egress security wanted to unseal the box of paper. I unsealed the box but got rather upset when they wanted to open the bag of paper. I balked, they agreed to just play feely-meely with the closed bag until they were satisfied that is was only paper inside. Arriving at SFO, to my surprise, Customs wanted to x-ray all my luggage for contraband fruit and meat, hence another hand-check fire-drill but this time they didn't want to open the box. End of story, I hope.