How can I eliminate this intermittent error? -> Error while writing to "

Howdy,

I've been chasing my tail on this one for a while now.
Is this a bug?
Is there anything I can do to work around it?

I need to use echo to rewrite the body of certain messages.
But sometimes this works and sometimes it doesn't.
It seems to be highly reproducible.

The only difference I can see between using echo and using /bin/echo
seems to be the frequency of error.

I tried using a lock file ... that reduced the frequency of the error,
but did not eliminate it.

Here is a highly simplified recipe that can quickly reproduce this
problem:
        $ cat Error.rc
        LOGFILE=/dev/stderr
        VERBOSE=yes
        TEST_STRING="abcdefghijklmnopqrstuvwxyz"
        
        :0 fbw : echo_locker
        | echo "$TEST_STRING"
        ### repeat above two lines 18 times for good measure
        ... ... ... duplicate entries purged ... ... ...
        :0 fbw : echo_locker
        | echo "$TEST_STRING"
        
And the output from a test run:
        $ echo "any email" | procmail -pm  Error.rc
        
        procmail: [4428] Mon Nov  9 19:03:25 2009
        procmail: Assigning "TEST_STRING=abcdefghijklmnopqrstuvwxyz"
        
        procmail: Locking "echo_locker"
        procmail: Executing "echo,abcdefghijklmnopqrstuvwxyz"
        procmail: Unlocking "echo_locker"
        
        ... ... ... duplicate entries purged ... ... ...
        
        procmail: Locking "echo_locker"
        procmail: Executing "echo,abcdefghijklmnopqrstuvwxyz"
        procmail: Error while writing to "echo"
        procmail: Rescue of unfiltered data succeeded
        procmail: Unlocking "echo_locker"
        
          Folder: **Bounced**                                                   
      0

Any help will be appreciated.

-- 
JW Simpson <john(_at_)swajime(_dot_)com>
SwaJime's Cove℠

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