Code such as the following:

$(vertex).animate({ "fill-opacity": 1.0 }, "slow", "swing", function () { animateVertexQueue(vertexLabels); });

Does not cause the fill-opacity css property be changed as you would expect. Looking through the code the error is an omission from the cssNumber property, it reads:

	cssNumber: {
		"zIndex": true,
		"fontWeight": true,
		"opacity": true,
		"zoom": true,
		"lineHeight": true,
		"widows": true,
		"orphans": true
	},

But should read:

	cssNumber: {
		"zIndex": true,
		"fontWeight": true,
		"opacity": true,
		"fillOpacity": true,
		"zoom": true,
		"lineHeight": true,
		"widows": true,
		"orphans": true
	},

That is with fillOpacity added as a flag. This stops "px" from being appended to the property value in the easing, which cause the property change to fail.