getAtomIndexAtCharIndex Fails?

I am looking for the bounding box around a string. I know that the string exists on a given line, i checked using TextLine.textBlock.content.text.

here is what I am doing

var tokens:Array = editor.text.split(myPattern); //myPatter is a RegExp,

//editor is a RichEditableText

var pos:int = 0;

for (var i:int=0;i<tokens.length-1;i++)

{

     var t:String = tokens;

     pos += t.length;

     var span:SpanElement = editor.textFlow.findLeaf(pos) as SpanElement;

     var relativePosition:int = pos - span.getAbsoluteStart();

     //var length:int = pos+searchInput.text.length;

     var bbox:Rectangle = spanBBox(span,pos,relativePosition,search.length);

     /// the rectangle is then used to place sprites  etc,,,

     pos += searchInput.text.length; // searchInput is TextInpu

}

private function spanBBox(abs:int,rel:int,len:int):Rectangle

{

     var line:TextFlowLine = editor.textFlow.flowComposer.findLineAtPosition(abs);

     var textLine:TextLine = line.getTextLine(true);

     if(textLine.textBlock.content.text.substring(rel,rel+len) != searchInput.text)

     {

          //this does happen, yet the line does contain the searchInput!

          rel = textLine.textBlock.content.text.indexOf(searchInput.text);

     }

     var atomIndex1:int = textLine.getAtomIndexAtCharIndex(rel);

     var atomIndex2:int = textLine.getAtomIndexAtCharIndex(rel+len);

     var r1:Rectangle = textLine.getBounds(editor);

     var bbox1:Rectangle = textLine.getAtomBounds(atomIndex1);

     var bbox2:Rectangle  = textLine.getAtomBounds(atomIndex2);

     bbox1.y = r1.y; bbox1.height = r1.height; bbox1.width = bbox2.x - bbox1.x;

     bbox1.x += textLine.x;

     return bbox1;

}

50% of the time atomIndex1,2 are -1. Any clues?

Thank you

Raed