QTableView::setRootindex(const QModelIndex& index) still counts rows of model in vertical header not children of index

When setting a hierarchical QStandardItemModel of the form

• Item 1
• Item 1a
• Item 1b
• Item 1c
• Item 2
• Item 2a
• Item 2b
• Item 2c

to a QTableView and then changing the root e.g. to Item 1 with table->setRootIndex(item1->index()) the QTableView still counts the rows of the first-level-items in the vertical header.

See attached screenshot that has been created with the attached program contained in the cpp file.
The QHeaderView attached to the QTableView stops at two when it should count to three (amount of child items)