QSortFilterProxyModel::parent(...) causes a SIGSEGV

Situation and how to reproduce

The single file application in attachment main.cpp shows a dialog with a edit and tree-view.
The tree-view has all nodes automatically expanded using a function expandTreeView(...).

When typing the letter 's' in the edit widget the filter is applied and the SIGSEGV signal is generated.

Omitting the expandTreeView(...) function and manually expanding each node and
also typing the 's' character in the edit widget works just fine.

REMARK: If an argument is added on the applications command line the 's' key press event is simulated.

Observation

The QTreeView::expand() method is probably messing up something but I just can't quite put my finger on it looking strolling through the source code in my debugger

What is clear is that in: QSortFilterProxyModel::parent qsortfilterproxymodel.cpp:2211
"it->key()" breaks and "it" is a result of "d->index_to_iterator(child)" which returns an invalid iterator.