QSortFilterProxyModel and a sourceModel with fetchMore causes wrong expansion of indexes

When using a `QTreeView` with a QSortFilterProxyModel, if the `sourceModel` has a `fetchMore` implemented, the items will expand automatically on a strange pattern.

When selecting a 3rd level item, the 1st level item of the same row as the 3rd level item's parent will be expanded. So in the example code attached to the issue, selecting "Item #4 / Item #3 / Item #0" will expand "Item # 3" on the top level, selecting "Item #4 / Item #2 / Item #0" will expand "Item # 2" on the top level and so on.

I've tested this with Python 2.7 + PySide, Python 3.7 + PySide 2.15 and 6.1 in both Windows 10 and Centos-7 all yielding the same result.

There's also a Qt forum discussion about it: https://forum.qt.io/topic/128367/qabstractitemmodel-qsortfilterproxymodel-leads-to-random-item-expansion