I tried uninstalling FB and then reinstalling it based on the current download for the extension. If I attempt to Edit the Design, as soon as it displays the form it shows the fieldsets jacked up. If I cancel, it doesn't overwrite the errant code that I removed, but if I click finish, the code is once again inserted. This is without doing anything other than clicking on Edit Design and then clicking Finish. So something is going on right at the beginning.
Are some files opened during Edit Design that I don't know about that could have this coding problem embedded in them?
If I click ignore legend, the problem goes away (because the errant "<span class=" code is not inserted) in the legend tag as described in the original post.