weird bug in tr (translate or delete character)

[Arch Drone]

Hi,

recently I have accidentaly found this strage buggy behavior:
address@hidden:~/tmp$ ls
a
address@hidden:~/tmp$ echo "abcDEF.<>" | tr -d [:alpha:]
bcDEF.<>
address@hidden:~/tmp$ mv a b; ls
b
address@hidden:~/tmp$ echo "abcDEF.<>" | tr -d [:alpha:]
.<>

Coreutils 6.10,  furthermore I have positive confirmation from pc with 
Coreutils 6.12 on different distro.
This bug occurs only when there is a file named exactly "a" in the current 
directory. Everything's OK when there are files like  "aa", "aaa", "b", 
whatever. I hope this isn't false alert otherwise I'll feel awkward :)

Best wishes,
Archdrone