DragDrop of multiple items to Spark List is much slower than to Halo List

Steps to reproduce:
1. Drop 10000 items to Spark List

Actual Results:
Big delay,
Timeout RTE from time to time
Error: Error #1502: A script has executed for longer than the default timeout period of 15 seconds.
at spark.layouts.supportClasses::LinearLayoutVector/shiftBlockRight()[E:\dev\trunk\frameworks\projects\spark\src\spark\layouts\supportClasses\LinearLayoutVector.as:448]
at spark.layouts.supportClasses::LinearLayoutVector/insert()[E:\dev\trunk\frameworks\projects\spark\src\spark\layouts\supportClasses\LinearLayoutVector.as:485]
at spark.layouts::VerticalLayout/elementAdded()[E:\dev\trunk\frameworks\projects\spark\src\spark\layouts\VerticalLayout.as:1107]
at spark.components::DataGroup/http://www.adobe.com/2006/flex/mx/internal::itemAdded()[E:\dev\trunk\frameworks\projects\spark\src\spark\components\DataGroup.as:1281]
at spark.components::DataGroup/adjustAfterAdd()[E:\dev\trunk\frameworks\projects\spark\src\spark\components\DataGroup.as:1504]
at spark.components::DataGroup/http://www.adobe.com/2006/flex/mx/internal::dataProvider_collectionChangeHandler()[E:\dev\trunk\frameworks\projects\spark\src\spark\components\DataGroup.as:1427]
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at mx.collections::ListCollectionView/dispatchEvent()[E:\dev\trunk\frameworks\projects\framework\src\mx\collections\ListCollectionView.as:1024]
at mx.collections::ListCollectionView/addItemsToView()[E:\dev\trunk\frameworks\projects\framework\src\mx\collections\ListCollectionView.as:1137]
at mx.collections::ListCollectionView/listChangeHandler()[E:\dev\trunk\frameworks\projects\framework\src\mx\collections\ListCollectionView.as:1284]
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at mx.collections::ArrayList/internalDispatchEvent()[E:\dev\trunk\frameworks\projects\framework\src\mx\collections\ArrayList.as:673]
at mx.collections::ArrayList/addItemAt()[E:\dev\trunk\frameworks\projects\framework\src\mx\collections\ArrayList.as:394]
at mx.collections::ListCollectionView/addItemAt()[E:\dev\trunk\frameworks\projects\framework\src\mx\collections\ListCollectionView.as:596]
at spark.components::List/dragDropHandler()[E:\dev\trunk\frameworks\projects\spark\src\spark\components\List.as:1679]
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at mx.core::UIComponent/dispatchEvent()[E:\dev\trunk\frameworks\projects\framework\src\mx\core\UIComponent.as:11804]
at mx.managers.dragClasses::DragProxy/_dispatchDragEvent()[E:\dev\trunk\frameworks\projects\framework\src\mx\managers\dragClasses\DragProxy.as:355]
at mx.managers.dragClasses::DragProxy/mouseUpHandler()[E:\dev\trunk\frameworks\projects\framework\src\mx\managers\dragClasses\DragProxy.as:580]

or

Error: Error #1502: A script has executed for longer than the default timeout period of 15 seconds.
at spark.components::List/get selectedIndices()
at spark.components::List/adjustSelection()[E:\dev\trunk\frameworks\projects\spark\src\spark\components\List.as:1872]
at spark.components::List/itemAdded()[E:\dev\trunk\frameworks\projects\spark\src\spark\components\List.as:810]
at spark.components.supportClasses::ListBase/dataProvider_collectionChangeHandler()[E:\dev\trunk\frameworks\projects\spark\src\spark\components\supportClasses\ListBase.as:1208]
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at mx.collections::ListCollectionView/dispatchEvent()[E:\dev\trunk\frameworks\projects\framework\src\mx\collections\ListCollectionView.as:1024]
at mx.collections::ListCollectionView/addItemsToView()[E:\dev\trunk\frameworks\projects\framework\src\mx\collections\ListCollectionView.as:1137]
at mx.collections::ListCollectionView/listChangeHandler()[E:\dev\trunk\frameworks\projects\framework\src\mx\collections\ListCollectionView.as:1284]
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at mx.collections::ArrayList/internalDispatchEvent()[E:\dev\trunk\frameworks\projects\framework\src\mx\collections\ArrayList.as:673]
at mx.collections::ArrayList/addItemAt()[E:\dev\trunk\frameworks\projects\framework\src\mx\collections\ArrayList.as:394]
at mx.collections::ListCollectionView/addItemAt()[E:\dev\trunk\frameworks\projects\framework\src\mx\collections\ListCollectionView.as:596]
at spark.components::List/dragDropHandler()[E:\dev\trunk\frameworks\projects\spark\src\spark\components\List.as:1679]
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at mx.core::UIComponent/dispatchEvent()[E:\dev\trunk\frameworks\projects\framework\src\mx\core\UIComponent.as:11804]
at mx.managers.dragClasses::DragProxy/_dispatchDragEvent()[E:\dev\trunk\frameworks\projects\framework\src\mx\managers\dragClasses\DragProxy.as:355]
at mx.managers.dragClasses::DragProxy/mouseUpHandler()[E:\dev\trunk\frameworks\projects\framework\src\mx\managers\dragClasses\DragProxy.as:580]

Expected Results:
Halo like performance

Workaround (if any):