[exim] Subject Rewritting and Spam Assassin

I'm running SA3.0.3 & Exim 4.51

In my Exim config, I've got:

acl_check_data:
  warn  message = X-Spam-Score: $spam_score
        spam = nobody:true

  warn  message = X-Spam-Report: $spam_report
        spam = nobody:true

  deny  message = This message exceeded the SpamAssassin threshold
        spam = nobody:true
        condition = ${if >{$spam_score_int}{100}{1}{0}}

  warn  message = Subject: ??? SPAM ??? $h_subject
        spam = nobody:true
        condition = ${if >={$spam_score_int}{50}{1}{0}}

accept


When I receive my mail and look at the SMTP headers, I've actually got two Subject: headers, the original and a re-written header. This is confusing our MUAs as they don't know which one to work with.

What am I doing wrong to cause there to be two Subject: headers ?

Thanks,

GTG

Gordon Ross,
Network Manager/Rheolwr Rhydwaith
Countryside Council for Wales/Cyngor Cefn Gwlad Cymru