Scrollbar jumping to top when shifting rows in QTableView

sb10q

The following program will intermittently enter a failure mode where the scrollbar jumps at the top whenever a new row is added (and the first one discarded). The failure mode is sometimes triggered by the main window losing and reacquiring focus. How do I fix this bug?

import sys
from PyQt5 import QtCore, QtWidgets


class _Scroller(QtCore.QAbstractTableModel):
    def __init__(self, parent):
        QtCore.QAbstractTableModel.__init__(self, parent)

        self.headers = ["Test"]
        self.depth = 20
        self.entries = []
        self.counter = 0

        timer = QtCore.QTimer(self)
        timer.timeout.connect(self.timer_tick)
        timer.start(100)

    def headerData(self, col, orientation, role):
        if (orientation == QtCore.Qt.Horizontal
                and role == QtCore.Qt.DisplayRole):
            return self.headers[col]
        return None

    def rowCount(self, parent):
        return len(self.entries)

    def columnCount(self, parent):
        return len(self.headers)

    def insertRows(self, position, rows=1, index=QtCore.QModelIndex()):
        self.beginInsertRows(QtCore.QModelIndex(), position, position+rows-1)
        self.endInsertRows()

    def removeRows(self, position, rows=1, index=QtCore.QModelIndex()):
        self.beginRemoveRows(QtCore.QModelIndex(), position, position+rows-1)
        self.endRemoveRows()

    def timer_tick(self):
        to_add = [self.counter]
        self.counter += 1

        nrows = len(self.entries)
        self.entries.extend(to_add)
        self.insertRows(nrows, len(to_add))
        if len(self.entries) > self.depth:
            start = len(self.entries) - self.depth
            self.entries = self.entries[start:]
            self.removeRows(0, start)

    def data(self, index, role):
        if index.isValid():
            if role == QtCore.Qt.DisplayRole:
                return str(self.entries[index.row()])


def main():
    app = QtWidgets.QApplication(sys.argv)

    w = QtWidgets.QMainWindow()
    table = QtWidgets.QTableView()
    w.setCentralWidget(table)
    w.show()

    table.setModel(_Scroller(table))

    sys.exit(app.exec_())


if __name__ == '__main__':
    main()