QML: Странный глюк в моей модели ?

class cl_List_model(QAbstractListModel):
    def __init__(self, items, parent=None):
        QAbstractListModel.__init__(self, parent)
        self._items = items
        self._all_items = items[:]
        self._search_str = ''
 
    def roleNames(self):
        return {Qt.UserRole + 0: QByteArray(b'item_name'), Qt.UserRole + 1: QByteArray(b'item_selected')}
 
    def rowCount(self, parent=None):
        return len(self._items)
 
    def data(self, index, role=None):
        role = role or QModelIndex()
        if role == Qt.UserRole + 0:
            return self._items[index.row()]['item_name']
        if role == Qt.UserRole + 1:
            return self._items[index.row()]['item_selected']
 
    def setData(self, index, val, role=Qt.UserRole + 1):
        if role == Qt.UserRole + 1:
            self._items[index.row()]['item_selected'] = not self._items[index.row()]['item_selected']
            self.dataChanged.emit(index, index, Qt.UserRole + 1)
            return True
        return False

>>> first = [1,2,3]
>>> second = first[:]
>>> first[0]=0
>>> first
[0, 2, 3]
>>> second
[1, 2, 3]
>>> first = [[1,2],[1,2]]  # mutable type !!!
>>> second = first[:]
>>> first[0].append(3)
>>> first
[[1, 2, 3], [1, 2]]
>>> second
[[1, 2, 3], [1, 2]]
>>> from copy import deepcopy
>>> first = [[1,2],[1,2]]
>>> second = deepcopy(first)
>>> first[0].append(3)
>>> first
[[1, 2, 3], [1, 2]]
>>> second
[[1, 2], [1, 2]]