I played with blend modes and discovered this:
public static readonly BlendState AlphaBlend = new BlendState("BlendState.AlphaBlend", Blend.One, Blend.InverseSourceAlpha);
(Microsoft.Xna.Framework.Graphics.BlendState.cs)
It does not look like an alpha blend because the sourceBland should be the Blend.SourceAlpha not the Blend.One
Is it a bug? Should I report It?