The man-page for grep writes:

       --line-buffering
              Use line buffering, it can be a performance penality.

But grep --help says:

      --line-buffered       flush output on every line

At least, the spelling is different. (And the description in the man-page is not as descriptive as in `grep --help\': I don\'t understand the man-page\'s description of the option, but I do inderstand the other.)

---
$ grep --line-buffering a
grep: unrecognized option `--line-buffering\'
Usage: grep [OPTION]... PATTERN [FILE]...
Try `grep --help\' for more information.

---
rpm -qf /usr/share/man/man1/grep.1.bz2
grep-2.5.1-alt0.2.cvs