Why is AudioSettings.DspTime so inaccurate?

AudioSettings.DspTime doesn't update every frame or anywhere close to it!

The manual says dspTime is ".. much more precise than the time obtained via the Time.time property." but, if I read DspTime every frame I can see that it stays the exact same value for up to 3-4 frames at a time. Even if I put this code in FixedUpdate (50 fps) it still doesn't change every frame.

Example Code...

 double lastDspTime = 0;
 
 void Update ()
 {
     if (AudioSettings.dspTime == lastDspTime)
     {
         Debug.Log ("Duplicate Time: " + lastDspTime);
     }
     lastDspTime = AudioSettings.dspTime;
 }

My output looks like this...

 ...
 Duplicate Time: 210.474666666667
 Duplicate Time: 210.474666666667
 Duplicate Time: 210.496
 Duplicate Time: 210.517333333333
 Duplicate Time: 210.517333333333
 Duplicate Time: 210.517333333333
 Duplicate Time: 210.538666666667
 Duplicate Time: 210.56
 Duplicate Time: 210.56
 ...

I couldn't find anyone else asking about it. Is it just me or do other people just not realize or care? Is there some way to fix this?

Unity 5.3.3 & 4.3.2 both do it.