QStandardItemModel::setItem makes the QPersistentModelIndexindex of the row Item invalid.

As per the documentation of QPersistentModelIndex, the item should retain the value of the QPersistentModelIndex until the row item is deleted.

QStandardItemModel *model;
model = new QStandardItemModel;

QStandardItem *item = new QStandardItem();
item->setData(QString("Text 1"), Qt::DisplayRole);
model->appendRow(item);

QStandardItem *item2 = new QStandardItem();
item2->setData(QString("Text 2"), Qt::DisplayRole);
model->appendRow(item2);

QStandardItem *item3 = new QStandardItem();
item3->setData(QString("Text 3"), Qt::DisplayRole);
model->appendRow(item3);

QPersistentModelIndex index = model->index(1,0);

QStandardItem *newItem = new QStandardItem;
newItem->setData("changed text", Qt::DisplayRole);
model->setItem(1, newItem);

//index is now invalid