This is not a bike touring and camera issue, but just a flash memory issue. Flash memory cards are not immune to directory corruption. Doesn't happen often, and may be the source of rumors about xray machines, but it does happen (I speak from experience). Picture Rescure (for the Mac)(prosofteng.com) is a file recovery program designed to work with Flash Memory cards. PCs have comparable programs, I just don't know any names. You don't need to own it, now, but be aware this type of software exists should you need it.
Mike