QSqlQueryModel in a QML view causes items being shown twice

[doom_Oo7]

I am in the process of learning both QtSql and QML, so there is some room for errors.
Pretty much my whole problem is in the title of my question.
I tried to make a short, self-contained code to reproduce it :

C++ code :
@
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QtQuick2ApplicationViewer viewer;
// uncomment after first launch, deleted test to make code short
// QFile::remove("my.db.sqlite");

QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName("my.db.sqlite");
db.open();

QSqlQuery create("create table List (sample_text char(200))");
QSqlQuery create2("insert into List values ("message !")");
create.exec();
create2.exec();

QSqlQueryModel *someSqlModel = new QSqlQueryModel();
someSqlModel->setQuery("SELECT * FROM List");

QQmlContext *context = viewer.rootContext();
context->setContextProperty("datamodel", someSqlModel);

viewer.setMainQmlFile(QStringLiteral("qml/test/main.qml"));
viewer.showExpanded();

return app.exec();
}
@

QML Code :

@ Rectangle {
ListView {
width: 200; height: 200
model: datamodel
delegate: Row {
Rectangle {
width: 100; height: 40
Text {
anchors.fill: parent
text: display
}
}
}
}
}

@
I should get "message !" as output in my list, but I get :

message !

message !

Any help ? Thanks!