New line return in windows Notepad

What version of AIR are you using? What is your code for saving out the text file?

I made a quick example file testing this and it seems to work fine. I am using Flash CC 2015 and AIR 17.0.0.124 for Desktop and am working on a Mac Pro running Mac OS X 10.10.5 Yosemite. I created a new AIR FLA for desktop, created a dynamic TextField on the stage, gave it an instance name of "textfield_txt", set the text to "this is a bunch of line breaks" with a line break after each word (no spaces). Then I made a new layer and started coding up a File and FileStream objects to save the text from the TextField to an existing ".txt" text file on my desktop named "lineBreaks.txt". When my TextField was NOT set to Multiline for the "Behavior" property under "Paragraph" options in the Properties inspector, it rendered everything together as one long run on word. When I changed it to Multiline, it wrote to the .txt file with the line breaks. Here is my code:

import flash.events.Event;
import flash.events.IOErrorEvent;
import flash.filesystem.File;
import flash.filesystem.FileMode;
import flash.filesystem.FileStream;
import flash.text.TextField;

var textfield_txt:TextField;
var textFile:File = File.desktopDirectory;
textFile = textFile.resolvePath("lineBreaks.txt");

var fs:FileStream = new FileStream();
fs.open(textFile, FileMode.WRITE);// open for writing to the text file
fs.writeUTFBytes(textfield_txt.text);// write the .text String from the TextField into the File
fs.close();// close FileStream and then setup listeners for opening back up and reading new text data
fs.addEventListener(Event.COMPLETE, onFileLoaded);
fs.addEventListener(IOErrorEvent.IO_ERROR, onFileLoadFail);
fs.openAsync(textFile, FileMode.READ);// regular .open() doesn't seem to dispatch Event.COMPLETE for knowing it is ready for reading

function onFileLoaded(e:Event):void {
  trace(fs.readUTFBytes(fs.bytesAvailable));
}

function onFileLoadFail(e:IOErrorEvent):void {
  trace(e.toString());
}