Drag and drop between sections in ListView

I'm not understand how drag item between section. Inside section - ok This code works well in one section. In the commented section I tried to solve the problem, but I failed when I try to drag between sections the item disappears

DropArea {
    anchors { fill: parent; margins: 0 }

    onEntered: {
        var a = extModel.get(drag.source.DelegateModel.itemsIndex);
        var b = extModel.get(mouseArea.DelegateModel.itemsIndex);

        if (a.group === b.group) {
            extModel.move(drag.source.DelegateModel.itemsIndex, mouseArea.DelegateModel.itemsIndex, 1)
        } else {
            a.group = b.group;
            mouseArea.DelegateModel.model.items.setGroups(mouseArea.DelegateModel.itemsIndex, 1, ['items', 'filter']);
            drag.source.DelegateModel.model.items.setGroups(drag.source.DelegateModel.itemsIndex, 1, []);
        }
    }
}

Full code https://pastebin.com/TARJ68Xc