DrawTexture Alpha Question

I'm having issues with the results Graphics.DrawTexture that maybe someone has an answer for. Currently I'm attempting to take a texture w/ an Alpha channel and use DrawTexture to add it to a RenderTexture. The resulting RGB of the RenderTexture looks exactly as expected, the Alpha is another story. The texture I'm using is essentially a feathered brush ( a black circle with a blurred edge ). The image itself is just black square (128px on each side) with the alpha channel that is a black circle in the center of a field of white. Here's a view of the Alpha Channel:



When I call DrawTexture to add this to a RenderTexture (which has first been cleared and set to display as white) I end up with a render texture which contains a white alpha channel and a thin grey ring where the soft edge of my circle would be.



The following is the script I'm using to accomplish this:

Code (csharp):

1. public class RenderToTexture : MonoBehaviour {
2.  
3.     public Texture textureStamp;
4.     public RenderTexture renderTexture;
5.  
6.  
7.     // Use this for initialization
8.     void Start () {
9.         renderTexture.format = RenderTextureFormat.ARGBFloat;
10.         Debug.Log( "Format: "+renderTexture.format );
11.  
12.  
13.         ClearTexture( renderTexture );
14.         DrawToTexture( new Vector2( Screen.width/2, Screen.height/2 ) );
15.     }
16.    
17.     // Update is called once per frame
18.     void Update () {
19.    
20.     }
21.  
22.  
23.     void ClearTexture( RenderTexture rt )
24.     {
25.         RenderTexture.active = rt;
26.         GL.Begin( GL.QUADS );
27.         GL.Clear ( true, true, Color.red );
28.         GL.End();
29.        
30.         RenderTexture.active = null;
31.     }
32.  
33.     void DrawToTexture ( Vector2 pos ) {
34.  
35.         RenderTexture.active = renderTexture;
36.         GL.PushMatrix();
37.         GL.LoadPixelMatrix(0,Screen.width,Screen.height,0);
38.  
39.         Rect rect = new Rect (pos.x - textureStamp.width / 2, (renderTexture.height - pos.y) - textureStamp.height / 2, textureStamp.width, textureStamp.height);
40.         Graphics.DrawTexture (rect, textureStamp);
41.  
42.         GL.PopMatrix();
43.         RenderTexture.active = null;
44.  
45.     }
46. }

Any ideas what I might be doing incorrectly?