I use the Lifestyle theme and have the same problem. Whether using publicize or cutting and pasting manually, FB invariably selects the wrong thumbnail for it's preview. Annoyingly, it'll often not give me the option of then selecting the right thumbnail. Sometimes it'll even take an image off the sidebar (!) and use that as a preview.
I have tried pasting post links into the Facebook debugging tool and doing that reveals FB can actually see the proper thumbnail. But it doesn't actually fix anything (that I can see).
Incidentally, in posts with 2 or more images, the only way I can guarantee WP will recognize the correct image as my thumbnail in the post feed, is to make the desired image a featured image for that post.
ATA - hope you don't mind me jumping on your thread here.
My blog is: http://www.escapetoreality.org