Program: 54605
Project: 54605
Buggy source:
@Override public Widget createIssue(){
  htmlElement=DOM.getParent(RootPanel.getBodyElement());
  final SimplePanel positioner=new SimplePanel();
  positioner.setPixelSize(30,30);
  positioner.getElement().getStyle().setProperty("String_Node_Str","String_Node_Str");
  positioner.getElement().getStyle().setProperty("String_Node_Str","String_Node_Str");
  positioner.getElement().getStyle().setProperty("String_Node_Str","String_Node_Str");
  final HTML echo=new HTML();
  final Label sandbox=new Label();
  sandbox.sinkEvents(Event.ONMOUSEMOVE);
  sandbox.setPixelSize(300,300);
  sandbox.getElement().getStyle().setProperty("String_Node_Str","String_Node_Str");
  sandbox.getElement().getStyle().setProperty("String_Node_Str","String_Node_Str");
  Event.addNativePreviewHandler(new NativePreviewHandler(){
    public void onPreviewNativeEvent(    NativePreviewEvent event){
      NativeEvent nativeEvent=event.getNativeEvent();
      Element target=nativeEvent.getTarget();
      if (!sandbox.getElement().isOrHasChild(target) && !positioner.getElement().isOrHasChild(target)) {
        positioner.removeFromParent();
        return;
      }
switch (Event.as(nativeEvent).getTypeInt()) {
case Event.ONMOUSEMOVE:
        int absX=nativeEvent.getClientX() + Window.getScrollLeft();
      int absY=nativeEvent.getClientY() + Window.getScrollTop();
    RootPanel.get().add(positioner,absX,absY);
  echo.setHTML("String_Node_Str" + nativeEvent.getClientX() + "String_Node_Str"+ "String_Node_Str"+ nativeEvent.getClientY()+ "String_Node_Str"+ "String_Node_Str"+ positioner.getAbsoluteLeft()+ "String_Node_Str"+ "String_Node_Str"+ positioner.getAbsoluteTop());
break;
}
}
}
);
VerticalPanel vPanel=new VerticalPanel();
vPanel.add(new ControlPanel());
vPanel.add(echo);
vPanel.add(sandbox);
return vPanel;
}

Fixed version (ground truth):
@Override public Widget createIssue(){
  htmlElement=DOM.getParent(RootPanel.getBodyElement());
  final SimplePanel positioner=new SimplePanel();
  positioner.setPixelSize(30,30);
  positioner.getElement().getStyle().setProperty("String_Node_Str","String_Node_Str");
  positioner.getElement().getStyle().setProperty("String_Node_Str","String_Node_Str");
  positioner.getElement().getStyle().setProperty("String_Node_Str","String_Node_Str");
  final HTML echo=new HTML();
  final Label sandbox=new Label();
  sandbox.sinkEvents(Event.ONMOUSEMOVE);
  sandbox.setPixelSize(300,300);
  sandbox.getElement().getStyle().setProperty("String_Node_Str","String_Node_Str");
  sandbox.getElement().getStyle().setProperty("String_Node_Str","String_Node_Str");
  Event.addNativePreviewHandler(new NativePreviewHandler(){
    public void onPreviewNativeEvent(    NativePreviewEvent event){
      NativeEvent nativeEvent=event.getNativeEvent();
      Element target=Element.as(nativeEvent.getEventTarget());
      if (!sandbox.getElement().isOrHasChild(target) && !positioner.getElement().isOrHasChild(target)) {
        positioner.removeFromParent();
        return;
      }
switch (Event.as(nativeEvent).getTypeInt()) {
case Event.ONMOUSEMOVE:
        int absX=nativeEvent.getClientX() + Window.getScrollLeft();
      int absY=nativeEvent.getClientY() + Window.getScrollTop();
    RootPanel.get().add(positioner,absX,absY);
  echo.setHTML("String_Node_Str" + nativeEvent.getClientX() + "String_Node_Str"+ "String_Node_Str"+ nativeEvent.getClientY()+ "String_Node_Str"+ "String_Node_Str"+ positioner.getAbsoluteLeft()+ "String_Node_Str"+ "String_Node_Str"+ positioner.getAbsoluteTop());
break;
}
}
}
);
VerticalPanel vPanel=new VerticalPanel();
vPanel.add(new ControlPanel());
vPanel.add(echo);
vPanel.add(sandbox);
return vPanel;
}