That is most curious. I finally did unlink the original scan from the persons mentioned and then uploaded it again. But this time, the problem occurred from the start: see
http://www.wikitree.com/photo/jpg/Holtz-282-1 where the thumbnail is there, but the picture itself not.
Your link
http://www.wikitree.com/photo.php/7/7b/Holtz-282-1.jpg however does bring up the correct image. But for some reason this link is missing (or incorrect) in the editing page.
You are probably right. It may well have to do with the fact that I had to adjust the surname to just "Holtz" instead of "von Holtz", but this is actually how this person was registered at birth in the church. (In those days, surnames were not rigidly adhered to - we had to wait for Napoleon to enforce a bit more discipline in this area).