QPluginLoader::loadHints return "no hints set" but by default PreventUnloadHint is set

QPluginLoader by default have set QLibrary::PreventUnloadHint

On a new QPluginLoader Object loadHints returns "no hints set"

  QLibrary::LoadHints hints = loader.loadHints();
  qDebug() << hints;
  hints |= QLibrary::LoadHint::PreventUnloadHint;
  qDebug() << hints;
  loader.setLoadHints ( hints );
  qDebug() << loader.loadHints();

This code outputs
QFlags<QLibrary::LoadHint>()
QFlags<QLibrary::LoadHint>(PreventUnloadHint)
QFlags<QLibrary::LoadHint>(PreventUnloadHint)