gridster-overlay-fix.js

var overlay_fix_start = function() {
    $('.overlay_fix').show();
}

var overlay_fix_stop = function() {
    $('.overlay_fix').hide();
};

// initiate gridster with the above functions executed each time a drag is started / stopped
$(".gridster ul").gridster({
    widget_margins: [10, 10],
    widget_base_dimensions: [140, 140],
    draggable: {
        start: overlay_fix_start,
        stop: overlay_fix_stop
   }
});