Flex AdvancedDataGrid listItems strange behaviour

I have the following XML, that is the dataprovider (as a Hierarchicaldata) of an Advanced DataGrid:

public var reqData:XML = <root>
  <Requirement ID="REQ-GEN-0.1" title="exigence gen 1" description="blabla 01" testable="true"/>
  <RequirementSet ID="GUI REQ">
    <Requirement ID="REQ-GUI-1.1" title="exigence ihm 1" description="blabla 11" testable="true"/>
    <Requirement ID="REQ-GUI-1.2" title="exigence ihm 2" description="blabla 12" testable="false"/>
  </RequirementSet>
  <RequirementSet ID="PERF REQ">
    <Requirement ID="REQ-PERF-2.1" title="exigence perf 1" description="blabla 21" testable="true"/>
    <Requirement ID="REQ-PERF-2.2" title="exigence perf 2" description="blabla 22" testable="false"/>
    <Requirement ID="REQ-PERF-2.3" title="exigence perf 3" description="blabla 23" testable="true"/>
    <Requirement ID="REQ-PERF-2.4" title="exigence perf 4" description="blabla 24" testable="false"/>
    <Requirement ID="REQ-PERF-2.5" title="exigence perf 5" description="blabla 25" testable="false"/>
    <Requirement ID="REQ-PERF-2.6" title="exigence perf 6" description="blabla 26" testable="false"/>
  </RequirementSet>
  <RequirementSet ID="BUS REQ">
    <RequirementSet ID="BUS 1 REQ">
      <Requirement ID="REQ-BUS-3.1.1" title="exigence bus 1" description="blabla 311" testable="false"/>
      <Requirement ID="REQ-BUS-3.1.2" title="exigence bus 2" description="blabla 312" testable="true"/>
    </RequirementSet>
    <RequirementSet ID="BUS 2 REQ">
      <Requirement ID="REQ-BUS-3.2.1" title="exigence bus3" description="blabla 321" testable="true"/>
    </RequirementSet>
    <RequirementSet ID="BUS 3 REQ"/>
    <RequirementSet ID="BUS 4 REQ">
        <Requirement ID="REQ-BUS-3.4.1" title="exigence bus4" description="blabla 341" testable="false"/>
    </RequirementSet>
    <RequirementSet ID="BUS 5 REQ"/>
    <RequirementSet ID="BUS 6 REQ"/>
  </RequirementSet>
</root>;

And here is the AdvancedDataGrid part:

<mx:AdvancedDataGrid id="reqADGtest" displayItemsExpanded="true"
                                             width="95%" height="75%" horizontalCenter="0" 
                                             contentBackgroundAlpha="0.0" chromeColor="0xdbeaff"
                                             openDuration="500" dragEnabled="true" dropEnabled="true"
                                             dragMoveEnabled="true" editable="true"
                                             variableRowHeight="true" horizontalScrollPolicy="auto">
                <mx:columns>
                    <mx:AdvancedDataGridColumn dataField="@ID" headerText="ID"/>
                    <mx:AdvancedDataGridColumn dataField="@title" headerText="Titre"/>
                    <mx:AdvancedDataGridColumn dataField="@testable" headerText="Testable"/>
                    <mx:AdvancedDataGridColumn dataField="@description" headerText="Description"
                                                           editorUsesEnterKey="true"
                                                           wordWrap="true"/>
                </mx:columns>
            </mx:AdvancedDataGrid>

The problem is that when I look at the listItems' length of the AdvancedDataGrid, it is 19 at the creation, and then 16 that is totally wrong (22 items). I want to access to some items and I can't which is really annoying. Is it a bug or something?

NOTE:

To access items by rowIndex and columnIndex I'm doing the following:

var advancedDataGridListData:AdvancedDataGridListData = 
                IDropInListItemRenderer(listItems[event.rowIndex][event.columnIndex]).listData 
                as AdvancedDataGridListData;

IHierarchicalCollectionView(dataProvider).getChildren(
                advancedDataGridListData.item)

EDITED 23/02/2012

I tested your solution with event.item but unfortunatly this item was always null and I didn't understand why. So I looked deeper into the source code of AdvancedDataGridBaseEx and I found that this is a part of the Adobe source code):

// send event to create the new one
        var advancedDataGridEvent:AdvancedDataGridEvent =
            new AdvancedDataGridEvent(AdvancedDataGridEvent.ITEM_EDIT_BEGINNING, false, true);
        // ITEM_EDIT events are cancelable
        advancedDataGridEvent.columnIndex = columnIndex;
        advancedDataGridEvent.dataField = _columns[columnIndex].dataField;
        advancedDataGridEvent.rowIndex = rowIndex;
        dispatchEvent(advancedDataGridEvent);

You can see that the event.item is never filled!!!! Thanks Adobe... I will try your other solution then I give you feedback.

LAST EDIT

I solved my problem by using in my custom datagrid:

var xmlNode:XML = this.selectedItem as XML;

Solution

How about this

dataProvider.getChildren(event.item)

based on reading here: http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/mx/controls/AdvancedDataGridBaseEx.html#event:itemEditBeginning

Alternatively maybe this method would help (though it's protected so you may need to do a "monkey patch" to change the access control modifier from protected to public:

http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/mx/controls/AdvancedDataGridBaseEx.html#absoluteToVisibleIndices()

I think on the event.rowIndex and event.columnIndex it's essentially giving you absolute values but the listItems has it based on what's currently visible rather than the absolute positions. Not a direct answer I know but it's very late here.