locale / char class bug in GNU grep 2.5.1

[Benjamin Elijah Griffin]

Problem: with -i character classes are at least sometimes not case
insensitive. This seems to depend on locale setting.

Here is a sample of the problem in action. It is repeatable for me every
time. Prompt is ":r! ". The pattern should match for every case, instead
for the third case, with a character in [] which needs case folding and
with the LANG set, there is no match.

:r! cat /tmp/QZ
-0555 402200    Oct 27 12:56:11 2002    ./Digitial Camera/2002-10-30/wood Q.jpg
:r! grep -i 'wood.*q' /tmp/QZ || echo not found
-0555 402200    Oct 27 12:56:11 2002    ./Digitial Camera/2002-10-30/wood Q.jpg
:r! grep -i 'wood.*[q]' /tmp/QZ || echo not found
not found
:r! grep -i 'WOOD.*[Q]' /tmp/QZ || echo not found
-0555 402200    Oct 27 12:56:11 2002    ./Digitial Camera/2002-10-30/wood Q.jpg
:r! /bin/env -u LANG grep -i 'wood.*[q]' /tmp/QZ || echo not found
-0555 402200    Oct 27 12:56:11 2002    ./Digitial Camera/2002-10-30/wood Q.jpg
:r! echo LANG=$LANG
LANG=en_US.UTF-8
:r! grep --version
grep (GNU grep) 2.5.1

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My first instinct was this is a locale bug, but since grep seems to manage
case folding fine outside of character classes, it looks more like a grep
bug. This is running on a fairly stock RedHat 8.0 system, if it helps.

Benjamin