'cal 9 1752' and emacs calendar disagree

[Leon]

Hi there,

For some historical reasons¹, September 1752 is a special month that
has no 3 - 13 dates. As you can see, 'cal 9 1752' will gives

   September 1752   
Su Mo Tu We Th Fr Sa
       1  2 14 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30


While emacs calendar gives:

   September 1752    
Su Mo Tu We Th Fr Sa 
                1  2 
 3  4  5  6  7  8  9 
10 11 12 13 14 15 16 
17 18 19 20 21 22 23 
24 25 26 27 28 29 30

Is this a bug?

Footnotes: 
¹  http://www.farid-hajji.net/fun/cj-cal91752.html
-- 
Leon