BCW0006: WARNING: Assignment to temporary.

When the compiler goes through this javascript code, it gives me the warning "BCW0006: WARNING: Assignment to temporary." when I try to assign the z value of a Vector3 the only reference (useful) I found to this error is [this page][1] and it's not terribly helpful. ----------

#pragma strict
class Premades
{	
	/**
	 * Creates a Square piece where each block is a random color.
	 */
	static function square() : Vector3[,]
	{
		var output : Vector3[,] = square(1);
		for(var first : int = 0; first < 1; first++)
			for(var second : int = 0; second < 4; second++)
				output[first, second].z = randomColor();//<----Throws the warrning here
		return output;                      //BCW0006: WARNING: Assignment to temporary.
	}
	/**
	 * Creates a square piece where each block is a set color.
	 */
	static function square(c : int) : Vector3[,]
	{
		var output : Vector3[,] = new Vector3[1,4];
		//              X,Y,color
		output[0,0] = V(0,0,c); //   
		output[0,1] = V(0,1,c); //   B B
		output[0,2] = V(1,0,c); //   O B
		output[0,3] = V(1,1,c);//    ^origin
		return output;
	}
	/**
	 * There are better ways to get a random number.
	 */
	static function randomColor() : int
	{
		var result = 1;
		switch (  Mathf.Floor(  Random.Range(0, 2.9999)  )  )
		{
			case 0: result =  1; break;//red
			case 1: result =  2; break;//green
			case 2: result =  4; break;//blue
		}
		return result;// If I try to return inside the switch block,
	}                   //It gives an unreachable code warning
	/** Because I'm too lazy to type out Vector3 */
	static function V(X : int, Y : int, Z : int) : Vector3
	{	return Vector3(X, Y, Z);	}
}
----------
Can I ignore this warning? It compiles just fine, but will it actually assign the number correctly?
  [1]: http://permalink.gmane.org/gmane.comp.lang.boo.devel/5779