Question about uniq's treatment of spaces-only lines

[Sudarshan S Chawathe]

In brief, uniq seems to treat lines containing only spaces differently
when given the -f 1 option (compared to when given -f 0 or no -f
option).  My question is: Is this behavior intentional (or is it a bug
in the implementation or docs)?  I find it difficult to reconcile with
my understanding of the docs.

In more detail, consider a file in.txt with the following contents
(which can be reconstructed based on the descriptive line if mangled by
mailers):

Next 5 lines have, resp., 1, 2, 1, 2, and 1, blanks:
 
  
 
  
 
Last line

Given this input, the output of 'uniq -u -f 1 in.txt' is different from
that of 'uniq -u in.txt' and 'uniq -u -f 0 in.txt'.  (With -f 1, the
blanks-only lines are all removed, but not so with the others.)

I tested the above originally on the uniq from coreutils 8.32 but later
also on 9.1.42 (built from the git sources I just pulled a short while
ago) and both versions exhibit the same behavior.

Regards,

-chaw