QPainter ignores font weight for certain fonts

#include <QApplication>
#include <QWidget>
#include <QPainter>

class Widget : public QWidget
{
protected:
    void paintEvent(QPaintEvent *)
    {
        const auto weights = {
            QFont::Thin,
            QFont::ExtraLight,
            QFont::Light,
            QFont::Normal,
            QFont::Medium,
            QFont::DemiBold,
            QFont::Bold,
            QFont::ExtraBold,
            QFont::Black
        };

        QPainter p(this);
        p.fillRect(rect(), Qt::white);
        p.setPen(Qt::black);

        int y = 30;
        for (const auto weight : weights) {
            QFont f("Source Code Pro", 14, weight);
            Q_ASSERT(f.weight() == weight);

            p.setFont(f);
            p.drawText(5, y, QString("Qt Framework (%1)").arg(weight));
            y += p.fontMetrics().height();
        }
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    Widget w;
    w.setMinimumSize(200, 300);
    w.show();

    return a.exec();
}

~> fc-match monospace
SourceCodePro-Regular.ttf: "Source Code Pro" "Regular"
~> fc-match monospace:bold
SourceCodePro-Bold.ttf: "Source Code Pro" "Bold"
~> fc-list 'Source Code Pro'
/usr/share/fonts/source-code-pro/SourceCodePro-BoldIt.ttf: Source Code Pro:style=Bold Italic
/usr/share/fonts/source-code-pro/SourceCodePro-Light.ttf: Source Code Pro,Source Code Pro Light:style=Light,Regular
/usr/share/fonts/source-code-pro/SourceCodePro-ExtraLightIt.ttf: Source Code Pro,Source Code Pro ExtraLight:style=ExtraLight Italic,Italic
/usr/share/fonts/source-code-pro/SourceCodePro-Bold.ttf: Source Code Pro:style=Bold
/usr/share/fonts/source-code-pro/SourceCodePro-ExtraLight.ttf: Source Code Pro,Source Code Pro ExtraLight:style=ExtraLight,Regular
/usr/share/fonts/source-code-pro/SourceCodePro-Black.ttf: Source Code Pro,Source Code Pro Black:style=Black,Regular
/usr/share/fonts/source-code-pro/SourceCodePro-Semibold.ttf: Source Code Pro,Source Code Pro Semibold:style=Semibold,Regular
/usr/share/fonts/source-code-pro/SourceCodePro-LightIt.ttf: Source Code Pro,Source Code Pro Light:style=Light Italic,Italic
/usr/share/fonts/source-code-pro/SourceCodePro-Medium.ttf: Source Code Pro,Source Code Pro Medium:style=Medium,Regular
/usr/share/fonts/source-code-pro/SourceCodePro-It.ttf: Source Code Pro:style=Italic
/usr/share/fonts/source-code-pro/SourceCodePro-Regular.ttf: Source Code Pro:style=Regular
/usr/share/fonts/source-code-pro/SourceCodePro-MediumIt.ttf: Source Code Pro,Source Code Pro Medium:style=Medium Italic,Italic
/usr/share/fonts/source-code-pro/SourceCodePro-SemiboldIt.ttf: Source Code Pro,Source Code Pro Semibold:style=Semibold Italic,Italic
/usr/share/fonts/source-code-pro/SourceCodePro-BlackIt.ttf: Source Code Pro,Source Code Pro Black:style=Black Italic,Italic
~> eselect fontconfig list | grep \*
Available fontconfig .conf files (* is enabled):
  [5]   10-hinting-slight.conf *
  [18]  30-metric-aliases.conf *
  [19]  40-nonlatin.conf *
  [20]  45-generic.conf *
  [21]  45-latin.conf *
  [22]  49-sansserif.conf *
  [23]  50-user.conf *
  [24]  51-local.conf *
  [28]  60-generic.conf *
  [29]  60-latin.conf *
  [32]  65-nonlatin.conf *
  [37]  70-no-bitmaps.conf *