recepient's email address truncated

I use a procmail recipe like the following for a number of small lists:

ReplyTo = "Reply-To: `formail -xFrom:`"

:0 c
* ^(To|Cc):.*[email protected]
* ? formail -X"From " -xFrom: -xSender: -xReply-To: -xResent-From: \
      | /var/list/.bin/multigram -b1 -m -l 28668 \
        /home/myaccount/etc/listone.txt
{
    :0 c
    /home/myaccount/etc/listone/.

    :0 fwh
    | formail -I "Reply-To: $ReplyTo"
      :0A
      ! `cat /home/myaccount/etc/listone.txt`
}

Everything works fine for quite some time. Lately there were some 
occasional email bounces on *some users*, on *some* list mails (not 
consistent). The bounce shows that the recepient's email address was 
truncated (4-5 letters chopped off from the right side). Test mails 
from the same server machine to the same email address goes just fine.
I double checked the email list file for any non-ascii characters etc
and it was clean.

Because this is hardly repeatable, I am not sure what else I should look 
at? Any advice would be appreciated.

Z