grep locale off by one?

[P]

What in the name of holy collating orders
is going on below?


$ echo "Z" | grep "[a-z]"
$ echo "Y" | grep "[a-z]"
Y
$ echo "a" | grep "[A-Z]"
$ echo "b" | grep "[A-Z]"
b


I know LC_ALL=C "fixes it", and I understand the collating
order being case insensitive, but why the inconsistency,
on the first and last characters (a and Z
in this case). Is it an off by one? Version info follows.

$ rpm -q grep glibc pcre
grep-2.5.1-7
glibc-2.3.2-11.9
pcre-3.9-10


$ echo $LANG
en_IE.UTF-8


cheers,
Pádraig.