[Exim] string expansion in autoreply transport

hi there again!

i don't like autoresponders, but was asked to implement them, so i tried
it as i found on a website where they used a router and a transport for
delivery. the router condition works and mail is routed to my transport,
but the if the subject line includes more than two words or arbitrary
characters like äüö as we use here sometimes in Germany i get strange
failures :
<--------snipp-------------->
This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

   test@???
     Expansion of "${lookup mysql{SELECT a_subject FROM users WHERE
address='${quote_mysql:${local_part}@${domain}}' }{$value}}" in
address_mysql transport contains non-printing character 228
<--------snapp-------------->

my transport looks like this:

  address_mysql:
   driver   = autoreply
   from = "${local_part}@${domain}"
   to       = ${sender_address}
   subject  = ${lookup mysql{SELECT a_subject FROM users WHERE
address='${quote_mysql:${local_part}@${domain}}' }{$value}}
   text     = ${lookup mysql{SELECT a_text FROM users WHERE
address='${quote_mysql:${local_part}@${domain}}'}{$value}}

hm..? i'm using exim 4.12 /w tls /amavis / mysql /courier maildirs on
debian(woody)

any help would be appreciated

greetings
Malte