Why does grep output lines that seemingly don't match the expression? I am aware different locales affect character order but I thought the -o output below confirms this is not a problem here.

[aa@bb tmp]$ cat test
aa bb
CC cc
dd ee

[aa@bb tmp]$ grep [A-Z] test
aa bb
CC cc
dd ee
[aa@bb tmp]$ grep -o [A-Z] test
C
C
[aa@bb tmp]$ grep -E [A-Z] test
aa bb
CC cc
dd ee
[aa@bb tmp]$ grep -n [A-Z] test
1:aa bb
2:CC cc
3:dd ee
[aa@bb tmp]$ echo [A-Z]
[A-Z]
[aa@bb tmp]$ grep -V
GNU grep 2.6.3
...
[aa@bb tmp]$ bash --version
GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)