[Plugin: NextGEN Gallery] Selecting a Gallery Preview Image does nothing

I have a client running the latest version of ngg gallery who would like to be able to list multiple galleries on a page, and have each one displayed as a preview image. However, selecting a preview image appears to have no effect on how the gallery is initially displayed. When researching this most of what I found in the way of suggestions was from much earlier versions of the plugin that seemed to involve parameters that are no longer used for galleries (ie. using “extend” in the short code), but the option to select a preview image is still there. Am I missing something?

Thanks.