I can reproduce this effect using other ebooks, on another (windows) environment and with an older calibre version.
So, normally I open the image directly to see whether the changes are there and never really bothered to use the "Browse image" function other then to get a quick overview.
In this case I changed a lot of pictures and wanted to use the "Browse images" to see if I perhaps missed one and was stunned as it looked like hardly any of the pictures were changed (only the first).
Although I don't think that this is a major issue, it still is strange. But I can live with it
