[Plugin: Alkivia SidePosts] Thumbnail images not linking in

I’m using the wordpress media gallery to upload images, which generates thumbnail sized images (doesn’t it?). I’ve installed this plugin and set the option to ‘Excerpts with thumbnails’.

If I upload a new image file when I create the post, the thumbnail appears in the sidepost. However, if I select an image that I’ve previously uploaded to the gallery to add to the post, the thumbnail does not appear (even though the image appears in the post).

Is this the way the plugin works or is there a problem?

I would rather not have to re-upload images every time, because this means I will have duplicate files in the gallery. Also, it makes things more complicated for the person who will eventually be maintaining the site.