Regexp match bug in grep(1)

[Steffen Nurpmeso]

Hello,

the snippet

  cat <<_EOT |grep '\(POSIX\|C\|en_\(US\|GB\)\)\.\(UTF-8\|utf8\)'
  C
  en_US.utf8
  en_US.UTF-8
  POSIX
  _EOT

does not match on OpenBSD (the extended one does correctly).
Ciao,

--steffen
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