QSortFilterProxyModel and QListView - indexWidget get deleted when filtering

gistfile1.py

import PySide.QtGui as QtGui
import PySide.QtCore as QtCore


_DEFAULT_ITEM_SIZE = QtCore.QSize(100, 85)
_USER_ROLE = QtGui.QStandardItem.UserType + 1

class CustomItemWidget(QtGui.QWidget):
    def __init__(self, parent=None):
        super(CustomItemWidget, self).__init__(parent=parent)

        self.setAutoFillBackground(True)
        self.label_text = "None"
        self.installEventFilter(self)

    def eventFilter(self, obj, event):
        if event.type() == QtCore.QEvent.Type.DeferredDelete:
            print "QEvent.Type.DeferredDelete CustomItemWidget of:", self.label_text

        return False

    def paintEvent(self, event):
        painter = QtGui.QPainter(self)

        # Default brush and pen
        bg_brush = QtGui.QBrush(QtGui.QColor("#8C8C8C"))
        pen = QtCore.Qt.NoPen

        painter.save()
        painter.setPen(pen)
        painter.setBrush(bg_brush)
        painter.drawRoundedRect(self.rect(), 12, 12)
        painter.restore()

        # Paint the label text
        painter.save()
        painter.drawText(self.rect(), QtCore.Qt.AlignCenter, self.label_text)
        painter.restore()

    def setData(self, role, value):
        if role == QtCore.Qt.DisplayRole:
            self.label_text = value



class CustomItem(QtGui.QStandardItem):
    def __init__(self):
        super(CustomItem, self).__init__()

        self.number = None
        self.item_widget = CustomItemWidget()

    def data(self, role):
        if role == QtCore.Qt.DisplayRole:
            value = "DATA %s" % str(self.number)
            self.item_widget.setData(role, value)

            return value

        if role == QtCore.Qt.SizeHintRole:
            return _DEFAULT_ITEM_SIZE

        return QtGui.QStandardItem.data(self, role)



class CustomView(QtGui.QListView):
    def __init__(self, parent=None):
        super(CustomView, self).__init__(parent=parent)

        self.setViewMode(QtGui.QListView.IconMode)
        self.setResizeMode(QtGui.QListView.Adjust)

        self.data_model = QtGui.QStandardItemModel()
        self.proxy_model = QtGui.QSortFilterProxyModel(self.data_model)

        self.proxy_model.setSourceModel(self.data_model)
        self.setModel(self.proxy_model)

    def logIndexWidgets(self):
        print ""
        for row in range(self.proxy_model.rowCount()):
            index = self.proxy_model.index(row, 0)
            print "\t", index.data(), self.indexWidget(index)
        print ""

    def keyPressEvent(self, event):
        print "IndexWidgets BEFORE filtering:", self.logIndexWidgets()

        if event.key() == QtCore.Qt.Key_1:
            self.proxy_model.setFilterWildcard("*1*")
            print "filtering by:", self.proxy_model.filterRegExp()
        if event.key() == QtCore.Qt.Key_2:
            self.proxy_model.setFilterWildcard("*2*")
            print "filtering by:", self.proxy_model.filterRegExp()
        if event.key() == QtCore.Qt.Key_3:
            self.proxy_model.setFilterWildcard("*3*")
            print "filtering by:", self.proxy_model.filterRegExp()
        if event.key() == QtCore.Qt.Key_Backspace:
            self.proxy_model.setFilterFixedString("")
            print "filtering by:", self.proxy_model.filterRegExp()

        print "IndexWidgets AFTER filtering:", self.logIndexWidgets()

        QtGui.QListView.keyPressEvent(self, event)

    def addItem(self, item):
        self.data_model.appendRow(item)
        proxy_index = self.proxy_model.mapFromSource(item.index())

        self.setIndexWidget(proxy_index, item.item_widget)


if __name__ == '__main__':
    import sys
    qapplication = QtGui.QApplication(sys.argv)

    layout = QtGui.QVBoxLayout()
    window = QtGui.QDialog()
    window.setLayout(layout)

    view = CustomView(window)
    view.resize(800, 600)

    layout.addWidget(view)

    for i in range(0, 10):
        item = CustomItem()
        item.number = i
        view.addItem(item)


    window.show()

    sys.exit(qapplication.exec_())

This is using PySide 1.2.1 on Linux with Python 2.7.5