May have found some kind of solution - if I use 'create new hyperlink' the invisible rectangle option does stick, and the freezing doesn't seem to happen. If I use 'create hyperlink from url' the rectangle option doesn't stick, and the freezing happens on particular urls. Could be something in the url I gues - they are quite long links. So I'll just have to get out of the habit of using the second option. Thanks lots for your help.