QML font size changes after calling QApplication::font()

#include <QApplication>
#include <QFont>
#include <QQmlApplicationEngine>
#include <QQmlContext>

int main(int argc, char** argv) {
  QApplication app(argc, argv);

  QString app_name = "big";

  if (argc > 1 && app.arguments().at(1) == "small") {
    auto font = app.font();
    app_name  = "small";
  }

  QQmlApplicationEngine engine;
  engine.rootContext()->setContextProperty("app_name", app_name);
  engine.loadData(R"(
import QtQuick 2.10
import QtQuick.Controls 2.3

ApplicationWindow {
  title: app_name
  visible: true

  Text {
    text: "<b>Some text</b>"
  }
}
)");

  return app.exec();
}