I'm surprised that I'm the only one who seems to have this problem, but I have found at least one possible cause: there is a linked script file /j/functions.js?2011030 which contains, among other things:
if (top != self) {
top.location.replace(self.location.href);
}
So it really does seem to have a break-out-of-iframes script, unless I am misreading what this code is meant to do.