PlayerPrefs not storing string?

I need to use PlayerPrefs to store arrays of bytes for my game. For some reason, the string I save with PlayerPrefs doesn't come out with the same in length.

I.e.

 byte[] TestArray = new byte[256];
 for (byte i = 0; i < 256; i++)
 {
     TestArray[i] = i;
 }
 
 char[] charBuffer = new char[256];
 PlayerPrefs.SetString ("Storage", new string(charBuffer));
 
 PlayerPrefs.Save ();

 Debug.Log (new String(charBuffer).Length);
 Debug.Log (PlayerPrefs.GetString ("Storage").Length);

Log:

 256
 5

Is this possibly an issue with encoding?