QLocale date toString uses standalone name where plain name should be used

I use QLocale().toString(QDateTme::currentDateTime()).

One of our users reports that month name is spelled incorrectly in Russian.

Example: "17 Март 2021 г." instead of "17 марта 2021 г." as shown by OS in its clock.

Why does not this function just query string from OS? I've tried to reproduce it - it works fine for me. So for me - Qt queries it from OS, for that user - it uses some internal mechanism.