AddText does not add

Friends, I have now cleaned out everything which is not needed to demonstrate...

However, use this test file

// ReplaceParagraphs.jsx
// use test file ReplaceParagraphs.fm
#target framemaker
var gasUserVariables = ["#cats", "#dogs", "#HORSE", "#DUCKUMENT"];  
var goCurrentDoc = app.ActiveDoc;                // the current document
PutRefPageItems ("Ref-Variables", "");
function PutRefPageItems (category, itemName) { // ================================================
  var flowName = "FM-calc";
  var oFlow, oPara, tr, targetDoc = goCurrentDoc; 
  var j, replaceString;
  oFlow = targetDoc.FirstFlowInDoc;              // go to the relevant flow in (ref) page
  var notFound = true;
  while (oFlow.ObjectValid()) {
    if (oFlow.Name == flowName) {
      notFound = false;
      break; } 
      oFlow = oFlow.NextFlowInDoc;
  }
  if (notFound) {
    alert ("PutRefPageItems:\nFlow «" + flowName + "» does not exist in document\n"+ targetDoc);
    return false;
  }
  oPara = oFlow.FirstTextFrameInFlow.FirstPgf;
  tr = GetParagraphs (oPara, "Ref-Variables");    // paragraphs to be replaced
//? $.bp(true);
  replaceString  = "";
  for (j = 0; j < gasUserVariables.length; j++) {
    replaceString = replaceString + "\n" + gasUserVariables;  // \n gives new paragraphs
  }
  targetDoc.TextSelection = tr;                  // set up the text range to clear the original text
  targetDoc.Clear(0);                            // clear it
  tr.end.offset = 0;                              // 0, 1 create 'appended' paragraphs; 
                                                  // -1 inserts in previous ¶ with wrong format
  targetDoc.AddText(tr.end, replaceString);      // insert the new text
} // --- end PutRefPageItems
function GetParagraphs (oPara, type) { // =========================================================
  var pgfFmt;
  while (oPara.ObjectValid ()) {
    pgfFmt = oPara.Name;
    if (pgfFmt == type) {                        // skip this
      break;
    }
    oPara = oPara.NextPgfInFlow;
    continue;
  }                                              // we are now on the first of the relevant ¶
//? $.bp(true);
  var tr = new TextRange();
  tr.beg.obj =  oPara;                            // set up the starting text range as the very beginning
  tr.beg.offset = 0;
  while (oPara.ObjectValid ()) {
    pgfFmt = oPara.Name;
    if (pgfFmt == type) {                        // must not be interspearsed with other
      tr.end = new TextLoc (oPara, Constants.FV_OBJ_END_OFFSET - 1);  
      oPara = oPara.NextPgfInFlow;
      continue;
    }
    break;
  } 
  return tr; 
}

Lines 37 ... 39 are the 'crucial' ones.