Thanks for all the input guys!
I did eventually find out a way around this.
My feeble knowledge of js meant that it wasn't immediately apparent to me that I could create a separate listener for a change event from the input itself. So I have something like this:
var jform_wizard = document.getElementById("jform_wizard");
jform_wizard.onchange = function() {
var wizval = document.getElementById("jform_wizard").value;
setActiveDivs(wizval);
};
which means that an onclick event doesn't need to be added to the input itself.
Now I have another question related to jdom, and I'm hoping for better than 15 views and no responses this time. Wish me luck
Andy