I really don't see a way for "savegame:xx" to return an image from non-existent saved game file.
To me this looks like some form of ill-caching, but you'll see for yourself. I'm uploading (with creators consent) the very minimalistic version (cca 16MB) of the project which already manifests the problem. Steps to reproduce:
1, run game
2, save the position
3, go to different view
4, save the position over the saved one
5, choose load or save game -> the thumbnail image is still from the step 2
6, restart the game - the image is now new and shiny
Link to the downloadable is in your PM.
Edit: one more thing, the caption of the image actually correctly changes so the description is taken from the right file.