Mike,
I think your user may just have a weird cached value or something. I just tested, and the popup showed your correct domain. Looking at the HTML on the page, there is no reference to /cms at all. Additionally, using the
Facebook URL Debug Tool
for that page, everything shows up right with no mention of /cms
I don't think you're crazy, don't worry. Stranger things have happened. However, please test with a different FB user and see if you think the problem still exists. My guess is that it's not really an issue, but I'll gladly be called out wrong on that.
I hope that helps,
Alex