Okay, I don't know what it was, but the filter as written below does work. Something else in the template was munged. I got it working by starting over with my original template before I tried to use the version compare filter and then adding the filter back in. This time it worked perfectly. Of course, I didn't bother to save the munged template before starting over, so I can't compare the munged template with the working template. What ever. It is working, That is all I wanted.