Hi Rob -
Thanks for looking into it. What's weird is that NO image showed up in my feed before I installed your plug-in.
After I installed your plug-in, and rebuilt the thumbnails, BOTH show up.
I'm going to try a new Blog post that does not have a featured image and take it from there. I'll let you know.
And in a weird side note, my wife has a completely unrelated blog on Squarespace, and for months her single image showed up in her feed perfectly. About the same time I noticed my duplicate issue, her feed began showing duplicate full images! And she changed nothing on her blog!
Maybe a Feedburner issue, as we both use that service?
I'll keep looking into it and let you know if I figure it out, find something else, or just plain give up!