tr depends on current directory?!

[Kelly Dean]

root@helpme:/# uname -a
Linux helpme 3.2.0-4-686-pae #1 SMP Debian 3.2.51-1 i686 GNU/Linux
root@helpme:/# echo foo | tr [a-z] [A-Z]
foo
root@helpme:/# cd usr
root@helpme:/usr# echo foo | tr [a-z] [A-Z]
FOO
root@helpme:/usr# cd ../home/
root@helpme:/home# echo foo | tr [a-z] [A-Z]
FOO
root@helpme:/home# cd ../root/
root@helpme:~# echo foo | tr [a-z] [A-Z]
foo
root@helpme:~# dash
# pwd
/root
# echo foo | tr [a-z] [A-Z]
foo
# cd ../usr
# echo foo | tr [a-z] [A-Z]
FOO
# tr --version
tr (GNU coreutils) 8.13
...

Somebody, please tell me I'm not drooling on myself in a straightjacket in a 
padded room.

Oh, I just discovered that the coreutils manual (even though not the tr man 
page) says gnu tr doesn't support brackets for ranges, which only ‟sometimes” 
work. But seriously, it's supposed to depend on the current directory?