I can see I'm not alone but I"ve been doing this for two years now and just last week I (1)shot the side of the the holder that I had already shot (On a trip to the Everglades no less) (2) realized I did so and that I ought to grab the holder again and try the shot again (3)Of course I now had a filmholder with two white sides showing and, while I thought I knew which one I had just exposed, I ended up with three shots on one negative and a blank negative.