QLocale::bcp47Name() not working as expected for "default" language-country combination

bcp47Name() doesn't print the expected dash-separated string codes when the QLocale::Country is the "default" for a given language. Examples:

QLocale locale(QLocale::English, QLocale::UnitedStates);
qDebug() << locale.bcp47Name(); //prints "en"

QLocale locale(QLocale::English, QLocale::UnitedKingdom);
qDebug() << locale.bcp47Name(); //prints "en-GB"

The same happens for all other languages.