That change should actually work in most cases. When I go to that page, in either http or https, and click the "FB Comments" box, I'm seeing the same comments on both pages. Additionally, I checked the fb:comments tag that we add, and they both look correct with the http version of the box.
Can you test again? Perhaps it was a caching issue that was still showing the old box temporarily. If not, let us know what you see on each page (no comments, no box at all, etc)?
Thanks,
Alex