Some magazines upside-down

Also, I don't know if it's related, but quite a few files don't have thumbnails at all in YACReader Library, whilst the thumbnails generate fine in Windows Explorer. See screenshot for example.

Any thoughts on why some covers appear the right side up in Windows explorer and any Windows apps, but appear upside-down in YACReader Library?

For the benefit of others - I managed to sort it with the help of Luis. Somehow the thumbnail library of YACReader Library had become corrupt We're not sure how that happened. What fixed it was removing the library, deleting the YACReader covers cache (a hidden folder), then adding the library again.