when files are copied to a flash drive, they are most likely sorted alphabetically. In Picasa I don't know what sorting options you chose by, but without looking at it, I would assume it is sorted by date. So whenever you open your flash drive in whatever computer you view them in, you will most likely need to sort by date. I cannot guarantee that will solve your problem as I cannot see the files. But just remember that files are always copied alphabetical regardless of the order they are in, in the application you are viewing them in. In other words you have to sort the files within the application you are viewing them. The order is not maintained from application to application.
i hope you find this information helpful.
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