error while writing to head?

Using the following recipe:

        # eliminate ugly fixed-length sig
        :0 fbw
        * ^TO_acting-pro
        * B ?? 
^--------------------------------------------------------------------------$
        * 1^1 B ?? ^.*$
        * -13^0
        | head -$=

I have a strange error:

        procmail: Executing "head,-87"
        procmail: Error while writing to "head"
        procmail: Rescue of unfiltered data succeeded

The full culprit message is attached.

Can it be reproduced?

-- 
Murphy's Guide to Science:
   If it's green or squirms, it's biology.
   If it stinks, it's chemistry.
   If it doesn't work, it's physics.

acting-pro.eml
Description: Text document