Senba has produced many proper thumbnails, and will probably rotate any image that comes out of his scanner downside up, before uploading. I have scanned many (acquired) photographs and was not bothered about the orientation, knowing that after scanning I would have to deal with the resulting jpeg anyway. As I cannot upload those scans here, because of copyright issues, I can't test whether a rotated scanned image would be treated differently from a non-rotated image, but I think chances would be very small that that would be the case.

A further thought - If a mobile device eg mobile phone is used and rotated it to take a photo, it may capture a rotated image and save it in a jpg file with an Exif orientation tag indicating that the photo is rotated.
Either one of these orientation tag values, 1, 8, 3 and 6 is often written to the jpg file when you take a photo by rotating a camera 0, 90, 180 and 270 degrees counter clockwise respectively.
If you view photos using an app supporting the Exif orientation, the app displays the photos properly by auto rotating them based on their orientation tag. But if you view photos in an application that does not support the Exif orientation, some photos are turned either upside down or sideways, exactly the way they are saved inside the files regardless of the orientation tag.
Looking at Senba's Exif data of his inverted photos it shows them being processed by a Canon MP990 which is a scanner of 1989 era. Could this be causing the inversion by being placed on scanner upside down and very old software producing the original thumbnail which IT system does eventually "correct" by accident by inverting the inversion?

Once downside up should logically remain downside up in three viewing modes.

Is this something to do with Senba's submissions /camera file rather than IT. Curious that a large number of his stock of thumbnails are downside up.

The thumbnail is wrong, then opening the picture shows the correct shot, but then going full screen the shots opens from the bottom to the top, instead of the normal way top to bottom sequence. Something for IT to have a look at.