Problems with the photo upload script have been reported a few times over the last year. Usually, this involves the script appearing to upload photos - but the thumbnails are never generated and the photos never appear in the database.
The newest version of the problem is that some thumbnails do not appear but the photos are uploaded.
If you upload 20 photos, you may get 12-13 thumbnails, leading you to believe that 7-8 never made it. But they are there.
Logging out & back in, and clearing the cache does not solve the problem. And I’ve experienced it on Safari and IE.