QQmlApplicationEngine engine slow to construct after installing custom message handler

[Chris_1981]

Calling QQmlApplicationEngine engine; needs around 8 seconds, if qInstallMessageHandler(myMessageOutput); is called before.
Without calling qInstallMessageHandler(myMessageOutput); it needs around 400 milliseconds. Used version is Desktop_Qt_5_6_0_MSVC2015_64bit-Debug.

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QElapsedTimer>

void myMessageOutput(QtMsgType type, const QMessageLogContext &context, const QString &msg)
{
  return;
}

int main(int argc, char *argv[])
{
  QGuiApplication app(argc, argv);
  
  qInstallMessageHandler(myMessageOutput); 
  
  QElapsedTimer timer;
  timer.start();
  QQmlApplicationEngine engine; // This line takes around 8 seconds. But without calling qInstallMessageHandler, it takes around 400 milliseconds. Why? 
  qint64 elapsed = timer.elapsed();

  engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

  return app.exec();
}