def filterAcceptsRow(self, row, parentindex):
        if not super(ReftrackSortFilterModel, self).filterAcceptsRow(row, parentindex):
            return False
        if parentindex.isValid():
            m = parentindex.model()
        else:
            m = self.sourceModel()
        i = m.index(row, 18, parentindex)
        reftrack = i.data(REFTRACK_OBJECT_ROLE)
        if not reftrack:
            return True
        else:
            return self.filter_accept_reftrack(reftrack)