QSortFilterProxyModel::mapFromSource returns a valid QModelIndex for the filtered out item

QSortFilterProxyModel::mapFromSource returns a valid QModelIndex for the child index of the filtered out item. In other words, if B is child of A in the source model and A filtered out by proxy model, QSortFilterProxyModel::mapFromSource returns a valid QModelIndex for B. But invalid QModelIndex for A.

Attached a project that demonstrates the problems (see assert).