Why does %c print 'M05' by default instead of 'May`?

[llimllib]

On my very standard mac computer:

$ biff time fmt -f '%c' now -1d
Sat, May 10, 2025, 10:44:39 AM EDT
2025 M05 12, Mon 22:07:33
2025 M05 11, Sun 22:07:33

date prints the format I would expect:

$ date
Mon May 12 22:09:43 EDT 2025

$ biff --version
Biff 0.1.0 (rev 2659045dba) (locale support enabled)

[BurntSushi]

Duplicate of #1