This is a typo, not particularly a bug. I'm not sure if this is exclusive to the data for "man grep" running at my university, but the manual text reads:
--line-buffered
Use line buffering, it can be a performance penality.
Clearly "penality" is a typo.
I hope this is helpful, it may be completely ungrounded, ie not the
"current" version of the man page, as I have very little knowledge of unix
development progress etc :)
Sincerely,
Chaz G
