createTextField + autoSize = infinite width/anger

Greetings!
Trying to accomplish the simplest thing ever… with no success.
I want to create a textfield (all scripted) with a specified width (420) and a varying height:

txt = this.createTextField("body_txt", this.getNextHighestDepth(), 0, 0, 420, 0);
txt.multiline = true;
txt.autoSize = true;
txt.text = text from xml going here........;

This code changes the width.
If I remove “autoSize”, I see no text (as the height is “0”);
WTF?
How do I keep the width the same as what I’ve set, and modify the height?
Thanks in advance for what I’m sure is a simple matter…

Steve