Thanks for your help. Because this happens on every map, (even brand new empty maps) and I uninstalled and reinstalled Mindjet, I realised that it must relate to my computer itself. In general I am having problems with its default fonts, and I feel that is being reflected with the program. I had hoped that there may have been a clean uninstall facility or something like that.
Unless you have any ideas relating the software, and not the map, I shall leave it at that.