Quick Controls 2 Material Theme font (Roboto) problem

[MCoder]

I created example project containig only one button and Material Theme. (using Wizard in Qt Creator)

Main.cpp:

#include <QGuiApplication>
#include <QQmlApplicationEngine>

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    return app.exec();
}

main.qml:

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.12

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    Button{
        text: "Test"
        highlighted: true
    }
}

qtquickcontrols2.conf:

[Controls]
Style=Material

[Material]
Primary=#1976D2
Accent=#FF5722

When I run thisaxample I see this:

Font on the button is very small and it is not Roboto font.
(family MS Shell Dlg 2, pixel size: 8)

I have installed Robot font in my system because if I add font family to button all works file.
main.qml:

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.12

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    Button{
        text: "Test"
        highlighted: true
        font.family: "Roboto"
        font.pixelSize: 14
    }
}

It is really Roboto font 14 px. But as I see in source code font is set in start of application.

http://code.qt.io/cgit/qt/qtquickcontrols2.git/tree/src/imports/controls/material/qquickmaterialtheme.cpp

Lets see... Font family and font size are set at startup.

Please tell me this is bug or I missing something?

Thank you.

P.S. My test system is: Qt 5.12.1, MinGW 7.3.0 64 bit, Windows 10

[MCoder]

Addition

But if I compile with Qt 5.9.7 all works fine.

main.qml:

import QtQuick 2.9
import QtQuick.Window 2.3
import QtQuick.Controls 2.2

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    Button{
        text: "Test"
        highlighted: true
    }
}

Only button text in uppercase.

Please tell me what difference and what I miss in new version?