RTE in Group during state change

RangeError: Index 0 is out of range.
at spark.components::Group/checkForRangeError()[E:\dev\4.0.0\frameworks\projects\spark\src\spark\components\Group.as:1106]
at spark.components::Group/setElementIndex()[E:\dev\4.0.0\frameworks\projects\spark\src\spark\components\Group.as:1265]
at spark.components::Group/addElementAt()[E:\dev\4.0.0\frameworks\projects\spark\src\spark\components\Group.as:1167]
at mx.states::AddItems/addItemsToContentHolder()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\states\AddItems.as:737]
at mx.states::AddItems/apply()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\states\AddItems.as:545]
at mx.core::UIComponent/applyState()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\core\UIComponent.as:10042]
at mx.core::UIComponent/commitCurrentState()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\core\UIComponent.as:9808]
at mx.core::UIComponent/setCurrentState()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\core\UIComponent.as:9701]
at mx.core::UIComponent/set currentState()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\core\UIComponent.as:6087]
at com.pronto.modules.im.view.widget.tree::TreeViewItemRenderer/set listData()[C:\Workspace-3.5.1\Pronto-clean\modules\im\src\com\pronto\modules\im\view\widget\tree\TreeViewItemRenderer.mxml:51]
at mx.controls::List/makeRowsAndColumns()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\controls\List.as:1417]
at mx.controls.listClasses::ListBase/scrollVertically()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\controls\listClasses\ListBase.as:7883]
at mx.controls.listClasses::ListBase/set verticalScrollPosition()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\controls\listClasses\ListBase.as:1695]
at mx.controls::List/configureScrollBars()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\controls\List.as:984]
at mx.controls.listClasses::ListBase/updateDisplayList()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\controls\listClasses\ListBase.as:4394]
at mx.controls::List/updateDisplayList()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\controls\List.as:1136]
at mx.controls::Tree/updateDisplayList()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\controls\Tree.as:1203]
at mx.controls.listClasses::ListBase/validateDisplayList()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\controls\listClasses\ListBase.as:3962]
at mx.managers::LayoutManager/validateDisplayList()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\LayoutManager.as:663]
at mx.managers::LayoutManager/doPhasedInstantiation()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\LayoutManager.as:736]
at mx.managers::LayoutManager/doPhasedInstantiationCallback()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\LayoutManager.as:1072]

Group.as, line 1099, checkForRangeError():
---------------------------------------------------------------------------
private function checkForRangeError(index:int, addingElement:Boolean = false):void
{
// figure out the maximum allowable index
var maxIndex:int = (_mxmlContent == null ? -1 : _mxmlContent.length - 1);

// if adding an element, we allow an extra index at the end
if (addingElement)
maxIndex++;

if (index < 0 || index > maxIndex)
throw new RangeError(resourceManager.getString("components", "indexOutOfRange", [index]));
}
---------------------------------------------------------------------------

I've got the following values of variables:
_mxmlContent = Array (...)
_mxmlContent.length = 0

So maxIndex is -1.

And then I get RTE from this:
---------------------------------------------------------------------------
if (index < 0 || index > maxIndex)
throw new RangeError(resourceManager.getString("components", "indexOutOfRange", [index]));
---------------------------------------------------------------------------

All this means that somehow "addingElement" is FALSE. It should be TRUE.

And here is the bug in code, Group.as, addElementAt():
---------------------------------------------------------------------------
public function addElementAt(element:IVisualElement, index:int):IVisualElement
{
...

// This handles the case where we call addElement on something
// that already is in the list. Let's just handle it silently
// and not throw up any errors.
if (host == this)

---------------------------------------------------------------------------

Example: http://mail.moscow.stalker.com/~maxim/groupBug/GroupRTETest.html
Steps to reproduce: scroll up and down and select different items. This can take some time.

Source: http://mail.moscow.stalker.com/~maxim/groupBug/srcview/index.html
Project FXP: http://mail.moscow.stalker.com/~maxim/groupBug/GroupRTETest.fxp