Hi,
thanks for your answer. Yes, I've updated the gallery and also cleared the cache. For me very interesting is the fact, that the new pictures is displayed always at the second position. I can change whatever I want. Always the same result. The link to the site:
The shortcode is
[gallery orderby="menu_order" ids="1764,1347,1232,1237,1239,1244,1242,1243,1245,1246"]
Picture number 1764 is the one, which should be the first (the new one). So you can see, the image order is correct.
Daniel