XNA 3rd Person Camera - pitch reverses when facing backwards?

I have a 3rd person camera which rotates around the Y axis fine (yaw) and when I am facing forward (0, 0, -1) moving the mouse up moves the camera up and down great. But the more I turn the player and camera the the less the camera moves up and down until I get to 90 degrees where it almost stay still and at 180 it moving the mouse up moves the camera down!

Any ideas? How should I be calculating camera pitch? The player only yaws - it does not roll or pitch. The camera yaws and pitches. The cameras update method looks like:

    public void Update(Vector3 playerPos, float pitch, float yaw)
    {
        Matrix rotation     = Matrix.CreateRotationY(yaw) * Matrix.CreateRotationX(pitch);
        Vector3 newOffset   = Vector3.Transform(offsetAmount, rotation);


        cameraPos   = playerPos + newOffset;
        View        = Matrix.CreateLookAt(cameraPos, playerPos, Vector3.Up);
        Projection  = Matrix.CreatePerspectiveFieldOfView(MathHelper.PiOver4, Constants.AspectRatio, Constants.NearClip, Constants.FarClip);
    }

Answer

Sounds alot like your Matrices are being multiplied in the wrong order. Try reversing the order of Multiplication to:

Matrix rotation = Matrix.CreateRotationX(pitch) * Matrix.CreateRotationY(yaw);