I have a QTableView combined with a QStandardItemModel.

The first section i the horizontal header of the QTableView has a Stretch resizeMode and the second one a Fixed resizeMode.

When QStandardItemModel::setItem is called, the resizeMode of the first section is reset to a Interactive resizeMode.

In the attached example, when you click the "Update" button, QStandardItemModel::setItem is called which sets a new item in the topleft cell of the table. At that moment you see the width of the first column changing because its sectionResizeMode has changed