[jQuery] IE: select change triggers pop-up blocker

[brian]

I have a wee bit of code that handles a select list change to load
some content via AJAX. In IE 7 & 8 (works a treat in 6!), clicking on
the select list triggers the pop-up blocker thingy. My code certainly
does not open a new window or anything like that:

$('#group_nav').change(function()
{
        var group_id = $(this).val();
        
        $.ajax({
                url:
                        '/admin/sections/alternative_nodes/' + group_id,
                success:
                        function(html)
                        {
                                $('#nav_admin').html(html);
                                
                                /* re-bind everything
                                 */
                                adminNavSetup();
                        }
        });
        return false;
});

adminNavSetup() is the function this block of code resides in.
However, commenting that out has no effect. Note that the select list
doesn't even open; a click is all it takes. Also, no request is made
to the server.

Anyone have an idea why the pop-up defense would be triggered like that?