Apparently my problem was that the mastheads that Xara provides include links to the Xara website (why would they do that?) Anyway the masthead link was being activated by my menu being so close to it. I don't know why they didn't tell me that last week when I submitted a ticket... last week they said that the only link on my site was the "made by Xara" link at the bottom.
I am grateful and relieved to know the problem, but very unhappy about the tons of hours I had to spend on it - I just hope this really does solve the problem and give a "heads up" to other users.