zsh "compctl -/" fails for Japanese directory names

Binary package hint: zsh

Old-style zsh filename completion using "compctl -/" fails for Japanese directory names.

To reproduce, let's make a few test directories. I'll be typing "cd <TAB>" to get zsh to autocomplete the name of the only directory in there. Actually, I will also use the completion for rmdir. Here we go:

@a2-s-34:~ % zsh -f (no rc files, use default zsh settings)
a2-s-34% echo $LANG
en_US.UTF-8
a2-s-34% mkdir TEST && cd TEST
a2-s-34% mkdir somedir
a2-s-34% cd somedir (completion worked)
a2-s-34% cd ..
a2-s-34% rmdir somedir (completion worked)
a2-s-34% mkdir 日本語
a2-s-34% cd 日本語 (completion worked)
a2-s-34% cd ..
a2-s-34% rmdir 日本語 (completion worked)
a2-s-34% compctl -/ cd
a2-s-34% mkdir somedir
a2-s-34% cd somedir (completion worked)
a2-s-34% cd ..
a2-s-34% rmdir somedir (completion worked)
a2-s-34% mkdir 日本語
a2-s-34% cd (completion FAILED)
a2-s-34% rmdir 日本語 (completion worked)

(rmdir still worked fine here, as it was not using "compctl -/")

Actually the first time this happened to me I was working inside a CIFS mount, and the kernel's CIFS module complained (in syslog) with "CIFS VFS: cifs_strtoUCS: char2uni returned -22".

This might be related :
http://www.zsh.org/mla/workers/2006/msg00548.html

Involved packages:
- zsh (4.3.2-25ubuntu1)
- linux-image-2.6.20-15-generic (2.6.20-15.27)
- smbfs (3.0.24-2ubuntu1.2)

Also occurs under Debian/etch with zsh 4.3.2-25 .

I guess it's about time for me to switch to new-style completion ^_^