Externally loaded sound - getBytesLoaded problem

Hey guys. ive run into this problem. this is my code

var clip:MovieClip = _root.createEmptyMovieClip("clip",getNextHighestDepth())
var mySound:Sound = new Sound()
mySound.loadSound("sounds/Ext_Bi_5.mp3",false)

//mySound.loadSound("sounds/Ext_Bi_5.mp3")
//mySound.loadSound("sounds/Ext_Bi_5.mp3",true)


clip.onEnterFrame = function(){
	trace(mySound.getBytesLoaded())
}

The Output is rather disturbing.
If i use mySound.loadSound(“sounds/Ext_Bi_5.mp3”,false) Then the trace in my onEnterFrame shows a getBytesTotal-value instead of the getBytesLoaded.

if i use mySound.loadSound(“sounds/Ext_Bi_5.mp3”) with no second parameter i get the same result as the first example.

BUT if i use mySound.loadSound(“sounds/Ext_Bi_5.mp3”,true) the trace Starts off showing the totalBytes but after about 10 iterations it starts to show the real getBytesLoaded-value.

Can anyone spot what im doing wrong here? why doesnt my trace show the getBytesLoaded-value? I can see that its not fully loaded using the bandwidth profiler…