That looks like a locale issue. Try running with LC_ALL=C in the environment.
- Bug in regexp in grep Grzegorz Woźniak
- Re: Bug in regexp in grep Paul Eggert
- Re: Bug in regexp in grep Grzegorz Woźniak
- Re: Bug in regexp in grep Paul Eggert
That looks like a locale issue. Try running with LC_ALL=C in the environment.