No, MJS, I didn't use a cable release. I don't even have one, because I found it impractical for field work. While there is a possibility that I caused some camera shake on my cheap tripod when I pressed the shutter release, I'm pretty smooth and careful about it.
As I mentioned, the difference wasn't noticable until I magnified the images 10 times, but the results were opposite of what I had expected.
Now you've got me wondering if I mixed them up, so I'll do it again for conformation.