I currently am trying to add a custom class which subclasses UIComponent to both a tree and a canvas, but when I try to re-order the tree by dragging I get this error:

TypeError: Error #1010: A term is undefined and has no properties. at mx.controls::Tree/get firstVisibleItem()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\controls\Tree.as:764] at flash.utils::ByteArray/writeObject() at flash.desktop::Clipboard/putSerialization() at flash.desktop::Clipboard/convertFlashFormat() at flash.desktop::Clipboard/setData() at mx.managers::NativeDragManagerImpl/doDrag()[C:\autobuild\3.2.0\frameworks\projects\airframework\src\mx\managers\NativeDragManagerImpl.as:282] at mx.managers::DragManager$/doDrag()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\managers\DragManager.as:243] at mx.controls.listClasses::ListBase/dragStartHandler()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\controls\listClasses\ListBase.as:9085] at flash.events::EventDispatcher/dispatchEventFunction() at flash.events::EventDispatcher/dispatchEvent() at mx.core::UIComponent/dispatchEvent()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\core\UIComponent.as:9298] at mx.controls.listClasses::ListBase/mouseMoveHandler()[C:\autobuild\3.2.0\frameworks\projects\framework\src\mx\controls\listClasses\ListBase.as:8822]

When I do not add the UIComponent to the canvas, this error does not occur, anyone have any knowledge as to why this happens?