Problems with UTF8 and docx (???)

[Jakob Curdes]

Hi, after about 10 years of using amavis quite without major problems I 
am now facing a strange issue.

We run "amavisd-new-2.7.0-pre14" on a fedora system defaulting to UTF-8. 
Since some time we have users complaining about docx documents that 
cannot be sent (but not all docx documents have this problem). When 
looking into the amavisd log, I see

Mar 29 17:17:27 xxx amavis[21041]: (21041-02) Checking: 9oiHPxyAyzpd 
[80.153.159.39] <xy at df.com> -> <er at df.de>
Mar 29 17:17:28 xxx amavis[21041]: (21041-02) (!!)TROUBLE in check_mail: 
check-banned FAILED: Malformed UTF-8 character (fatal) at 
/usr/local/sbin/amavisd line 4820.
Mar 29 17:17:28 xxx amavis[21041]: (21041-02) (!)PRESERVING EVIDENCE in 
/var/amavis/tmp/amavis-20110329T171654-21041-6eGAXmsw

When looking at the eMail I cannot see real problems.

I already found a hint that amavisd should not run in an UTF8 
environment and set some environment variables accordingly, see the 
amavisd start line:

  /usr/local/sbin/amavisd at montecristo.is-ol.de 
amavisd-new-2.7.0-pre14 (20110203), Unicode aware, LC_ALL="C", LANG="C"

... but still the only way to avoid the documents ending up as unsent 
mail is to disable banned checking altogether.
Our perl version is

perl, v5.8.8 built for x86_64-linux-thread-multi

What can I do to diagnose this further? Or does anybody have an idea 
what is going on here? It looks like it is specific to this environment 
as we have similar setups without this problem.

Thank you for a hint,
Jakob Curdes