Totally confused is ActionScript case sensitive

I am looking at code for a simple preloader

I have three frames in scene 1, frame 2 simply says: this.gotoAndPlay(1);, frame 3 says stop(); and here is the code for frame 1:

bytes_loaded=Math.round(this.getBytesLoaded());
bytes_total=Math.round(this.getBytesTotal());
getPercent=bytes_loaded/bytes_total;
this.loadbar._width=getPercent400;
this.Loadtext=Math.round(getpercent
100)+"%";
if(bytes_loaded==bytes_total){
this.gotoAndPlay(3);
}

loadbar - when I look in library it is called LoadBar and it is a movie clip
when I click on the movie clip and look under at properties panel it is called LoadBar?
If I double click on the LoadBar instance - inside the movie clip time line it says LoadBar?

confused :- (

If I change the code from

this.loadbar._width=getPercent*400

to -->

this.LoadBar._width = getPercent*400 (it works)

if I change the code to:

this.loadBar._width = getPercent*400 (it works)

if I change the code to:

this.loadbar._width = getPercent*400 (it works)

Similarly if I call it LOADBAR, or LOadBar, or LOadBAR or LOadBar etc it all works as expected

however if I call it loadb, or loady it does not work

I am very confused please, please help
How can this be case sensitive???