QLocale::system().monthName(3).simplified() segfaults

Testing with identical results on Gentoo Linux with its latest Qt 5.15.x and X11 and on Fedora Linux with Qt 5.15.9 under Wayland: QLocale::system().monthName(3).simplified() segfaults reproducible.

Example C++ file:

#include <QLocale>
#include <QDebug>

int main(int, char*[]) {
    qWarning() << QLocale::system().monthName(3);
    qWarning() << QLocale::system().monthName(3).trimmed();
    qWarning() << QLocale::system().monthName(3).simplified();
    return 0;
}

First two debug outputs (up to and including trimmed) work and print "March". Only last one crashes.

With Qt 6.4.3 on Fedora Linux, the same C++ program runs fine, prints three times "March".