This is likely the underlying OpenSeadragon javascript library picking up on some internal EXIF metadata and adjusting orientation proactively, which we actually don’t want. EXIF data - especially around image orientation - is a nightmare of inconsistency (this example is from a Canon camera, and Canon has its own EXIF metadata as well). For seadragons, we have even seen the EXIF metadata remain but the user rotating images manually, creating an image rotation that is fighting its own EXIF metadata.
If we begin to see a lot of this, we can create a ticket and look for consistent criteria for a fix. So far, this seems to be rare.
Um, small bonus points: I can correct the interpretation of the exif data on these. This kind of rotation was only an issue for a couple of weeks and should be fixed, so let me know if you come across more and I’ll get them right-side up. (You may need to refresh the page to see it corrected)