Program: 31750
Project: 31750
Buggy source:
public void commentOutText(){
  String highlightedTextArea=rSyntaxTextArea.getSelectedText();
  if (highlightedTextArea != null) {
    highlightedTextArea=findStartSymbol();
    if (highlightedTextArea.startsWith("String_Node_Str")) {
      rSyntaxTextArea.replaceSelection(highlightedTextArea.replace("String_Node_Str","String_Node_Str"));
    }
 else {
      String[] array=highlightedTextArea.split("String_Node_Str");
      StringBuilder commentedCodeBuilder=new StringBuilder();
      for (int i=0; i < array.length; i++) {
        array[i]="String_Node_Str" + array[i];
        if (i != array.length - 1) {
          array[i]=array[i] + "String_Node_Str";
        }
        commentedCodeBuilder.append(array[i]);
      }
      rSyntaxTextArea.replaceSelection(commentedCodeBuilder.toString());
    }
  }
 else {
    try {
      int currentOffsetFromLineStart=rSyntaxTextArea.getCaretOffsetFromLineStart();
      int currentCaretPosition=rSyntaxTextArea.getCaretPosition();
      int lineStartPosition=currentCaretPosition - currentOffsetFromLineStart;
      int lineLength=rSyntaxTextArea.getLineEndOffsetOfCurrentLine();
      String firstChar=rSyntaxTextArea.getText(lineStartPosition,lineLength - lineStartPosition);
      if (firstChar.startsWith("String_Node_Str")) {
        rSyntaxTextArea.replaceRange("String_Node_Str",lineStartPosition,lineStartPosition + 1);
      }
 else {
        rSyntaxTextArea.replaceRange("String_Node_Str",lineStartPosition,lineStartPosition);
      }
    }
 catch (    BadLocationException ex) {
      Exceptions.printStackTrace(ex);
    }
  }
}

Fixed version (ground truth):
public void commentOutText(){
  String highlightedTextArea=rSyntaxTextArea.getSelectedText();
  if (highlightedTextArea != null) {
    highlightedTextArea=findStartSymbol();
    if (highlightedTextArea.startsWith("String_Node_Str")) {
      rSyntaxTextArea.replaceSelection(highlightedTextArea.replace("String_Node_Str","String_Node_Str"));
    }
 else {
      String[] array=highlightedTextArea.split("String_Node_Str");
      StringBuilder commentedCodeBuilder=new StringBuilder();
      for (int i=0; i < array.length; i++) {
        array[i]=(array[i].charAt(0) == '%') ? array[i] : "String_Node_Str" + array[i];
        if (i != array.length - 1) {
          array[i]=array[i] + "String_Node_Str";
        }
        commentedCodeBuilder.append(array[i]);
      }
      rSyntaxTextArea.replaceSelection(commentedCodeBuilder.toString());
    }
  }
 else {
    try {
      int currentOffsetFromLineStart=rSyntaxTextArea.getCaretOffsetFromLineStart();
      int currentCaretPosition=rSyntaxTextArea.getCaretPosition();
      int lineStartPosition=currentCaretPosition - currentOffsetFromLineStart;
      int lineLength=rSyntaxTextArea.getLineEndOffsetOfCurrentLine();
      String firstChar=rSyntaxTextArea.getText(lineStartPosition,lineLength - lineStartPosition);
      if (firstChar.startsWith("String_Node_Str")) {
        rSyntaxTextArea.replaceRange("String_Node_Str",lineStartPosition,lineStartPosition + 1);
      }
 else {
        rSyntaxTextArea.replaceRange("String_Node_Str",lineStartPosition,lineStartPosition);
      }
    }
 catch (    BadLocationException ex) {
      Exceptions.printStackTrace(ex);
    }
  }
}