QLocale::setDefault without effect for number options

// setup a custom locale
QLocale customLocale( QLocale::English );
customLocale.setNumberOptions( QLocale::OmitGroupSeparator | QLocale::OmitLeadingZeroInExponent |
                               customLocale.numberOptions() );

// Set the custom locale as default
// https://doc.qt.io/qt-5/qlocale.html#setDefault
QLocale::setDefault( customLocale );

// using the custom locale directly
// https://doc.qt.io/qt-5/qlocale.html#toString-8
QString str1 = customLocale.toString( d );
qDebug() << str1;

// using the default locale which was set to be the custom locale is supposed to give the same output!
// https://doc.qt.io/qt-5/qlocale.html#QLocale
QLocale loc;
QString str2 = loc.toString( d );
qDebug() << str2;

// Arg is also supposed to use the default locale according to its documentation.
// https://doc.qt.io/qt-5/qstring.html#arg-9
QString str3 = QString( "%1" ).arg( d );
qDebug() << str3;

"5e-7"
"5e-07"
"5e-07"

"5e-7"
"5e-7"
"5e-7"