QWidget::setFixedSize() causes glitches when moving to another screen with a different DPI

Code

// widget.h
class Widget : public QWidget
{
    Q_OBJECT

public:
    Widget(QWidget* parent = nullptr) : QWidget(parent) {}

protected:
    void paintEvent(QPaintEvent*)
    {
        QPainter p(this);
        p.drawLine(0, 0, width(), height());
        p.drawLine(0, height(), width(), 0);
    }
};

// main.cpp
int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);  // Enabling/disabling this has no effect
    QApplication app(argc, argv);

    Widget win;
    win.setMaximumSize(600, 400);
    win.show();

    return app.exec();
}

Steps to reproduce

1. Set up 2 screens, with 125% scaling on the first and 100% on the second.
2. Build and run the attached project. Launch the application on the 125% screen.
3. Very gradually, move the window towards the second screen, until just after the window scaling changes
4. Very gradually, move the window towards the original screen

If the glitch doesn't occur on the first attempt, try a few more times.

Outcome
During both transitions, glitching occurs.

Scope of bug

• The issue also occurs if we replace setFixedSize() with setMinimumSize() and setMaximumSize(), giving the same sizes
• The issue does not occur if we replace setFixedSize() with resize()
• The issue does not occur in Qt 6

Workaround

Set a maximum size that is very close to (but not equal to) the minimum size:

win.setMaximumSize(601, 400);
win.setMinimumSize(600, 400);