DateField day abbreviation uses last letter

Version: 5.4.0

When a user clicks on the button generated by a DateField component, a calendar pops up to select a date. The abbreviation of the seven days are seven times 'y' in English. The abbreviation of each day uses the last letter instead of the first letter. E.g.: should be: "m t w t f s s" instead of "y y y y y y y" for English locale.