Quaternion rotation bug

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
using OpenTK;
 
namespace Cardio3D
{
  class Quaternion_Bug
  {
    public static void test()
    {
      Quaternion cameraQuaternion = Quaternion.Identity;
      float delta = 0.005f;
      for (float i = 0.0f; i <= Math.PI*2.1; i=i+delta)
      {
        Vector3 rotAxis = new Vector3(0.0f, 1.0f, 0.0f);
        Quaternion deltaQuat = Quaternion.FromAxisAngle(rotAxis, delta);
        cameraQuaternion = deltaQuat * cameraQuaternion;
 
        Vector3 axis = Vector3.Zero;
        float angle = 0.0f;
        System.Console.WriteLine("Cam quat: {0}", cameraQuaternion);
        //@tag Correction in a OpenTK bug?
        //if (cameraQuaternion.W < -1.0f)
        //{
        //  cameraQuaternion.W = -1.0f;
        //}
        cameraQuaternion.ToAxisAngle(out axis, out angle);
        axis.Normalize();
 
        //System.Diagnostics.Debug.Assert(!float.IsNaN(angle));
        if (float.IsNaN(angle))
        {
          throw new System.ApplicationException("Invalid rotation angle");
        }
 
        angle = OpenTK.MathHelper.RadiansToDegrees(angle);
 
        System.Console.WriteLine("Axis around: {0}", axis);
        System.Console.WriteLine("Axis rotation applied: {0}", angle); 
      }
    }
  }
}