Changes in TextField CS4->CS5

function setText(txt:String):void

{

//    var tf:TextFormat = instructionText.getTextFormat();

    instructionText.text = txt;

//    instructionText.setTextFormat(tf);

}

This code is from a TextField instance in a MovieClip in my library.  In CS4 it worked fine.  In CS5, if I don't do the above assignment, it displays the default text that's typed in when editing the instance in the library.  If I do do the assignment, then that field appears blank/empty.  If I uncomment the TextFormat statements above (which have worked in the past in CS3), it does nothing.