Pictures remain "New" when browsing with a photo viewer

In the "New" tab I have several new photos from a friend. I double-click the first one and it downloads and opens in my default picture viewer (in my case the "Windows Picture and Fax Viewer"). When I then use the viewer to navigate to the next picture, Wuala correctly downloads the next photo and hands it over to the viewer, however, Wuala won't mark the photo as "read", which results in the picture still being marked with a "New" star.