If you click on an area in the slider without dragging your mouse, it doesn't seem to trigger the onChange function. I tracked down the problem to occur within idrag.js in the dragstop method. dragged.dragCfg.init seems to be false in this case. I added a few extra lines to compare the current position and fire off the onChange function.

		if (dragged.dragCfg.init == false) {
			var nR = {
				x : parseInt(jQuery.css(dragged,'left')) || 0,
				y : parseInt(jQuery.css(dragged,'top')) || 0
			};
			if (dragged.dragCfg.onChange && (nR.x != dragged.dragCfg.oR.x || nR.y != dragged.dragCfg.oR.y)) {
				dragged.dragCfg.onChange.apply(dragged, dragged.dragCfg.lastSi||[0,0,nR.x,nR.y]);
			}
			return false;
		}