Reposting to Coraline Theme's forum as requested. (Thanks, WPyogi for the advice.)
(I have also since upgraded both WP and Coraline to make sure I'm using the most current version of each.)
According to Coraline description, "Coraline supports featured images (thumbnails for gallery posts and custom header images for posts and pages)" - I think that means the featured image is supposed to control the custom header when the image is large enough, but control the gallery thumbnail when it's smaller... but I can't find anywhere that explains how featured images are supposed to effect gallery images, and I haven't been able to figure out how to set the featured image for thumbnails - it seems to ignore the smaller files altogether.
The ultimate goal here is to have a REGULAR size image in the post, and a THUMBNAIL of that same image in the post excerpt - specifically for the Search Results page.
I thought I could use the gallery with ONE single image to accomplish this, instead of using an inserted non-gallery image.
Can someone help me understand how to accomplish this? Will it take a hack? Which files would I need to change to get a thumbnail on the post excerpt, and a full image on the post?