Auto-reply not being sent in some cases

I'm trying to send an autoreply to senders who leave the Subject: field of their message blank, telling them that my server rejects messages with blank subjects (because in my experience, such no-subject messages are either spam or not worth reading).  The autoreply works fine in test sends from Yahoo and from a mail client, but when I send from another host's webmail, I don't get the autoreply message.  There is no spam folder on the webmail, so that's not the problem.  I verified that I can send normal mail directly to the webmail, so I know the webmail is working properly.  The procmail logs show that the autoreply was sent, but I notice that the logfile lines are in a different order than for the case in which the autoreply was received.  (In the case where the autoreply wasn't received, "Folder:" precedes "Executing").  That's the only clue I have as to why messages from two different senders get the autoreply while messages from a webmail don't get the autoreply.  Here are the logs and code:

------------------------------------------------------------------------------
 Log of an unsuccessful autoreply.  Note that "Folder:" precedes "Executing"
------------------------------------------------------------------------------
procmail: Assigning "LASTFOLDER= (formail -r -k -A "X-Loop: [email protected]"  \
			   -A   "From: Michael B. <[email protected]> " ;\
			echo "(This is a prerecorded message.)  Your message was trashed and not received because $BOUNCE." ) | $SENDMAIL $SENDMAILFLAGS -t"
From [email protected]  Sun Jul 22 22:59:29 2012
 Subject: 
  Folder:  (formail -r -k -A "X-Loop: [email protected]	   1435
procmail: Executing " (formail -r -k -A "X-Loop: [email protected]"  \
			   -A   "From: Michael B. <[email protected]> " ;\
			echo "(This is a prerecorded message.)  Your message was trashed and not received because $BOUNCE." ) | $SENDMAIL $SENDMAILFLAGS -t"

------------------------------------------------------------------------------
 Log of a successful autoreply.  "Executing" precedes "Folder:"
------------------------------------------------------------------------------
procmail: Assigning "LASTFOLDER= (formail -r -k -A "X-Loop: [email protected]"  \
			   -A   "From: Michael B. <[email protected]> " ;\
			echo "(This is a prerecorded message.)  Your message was trashed and not received because $BOUNCE." ) | $SENDMAIL $SENDMAILFLAGS -t"
From [email protected]  Sun Jul 22 23:05:02 2012
procmail: Executing " (formail -r -k -A "X-Loop: [email protected]"  \
			   -A   "From: Michael B. <[email protected]> " ;\
			echo "(This is a prerecorded message.)  Your message was trashed and not received because $BOUNCE." ) | $SENDMAIL $SENDMAILFLAGS -t"
 Subject: 
  Folder:  (formail -r -k -A "X-Loop: [email protected]	    903

------------------------------------------------------------------------------
 Relevant part of my procmail code
------------------------------------------------------------------------------
	:0
	*$BOUNCE ?? (.)
	{	:0c
		| (formail -r -k -A "X-Loop: [email protected]" ; \
			   -A   "From: Michael B. <[email protected]> " ;\
			echo "(This is an automated message.)  Your message was trashed and not received because $BOUNCE." ) | $SENDMAIL $SENDMAILFLAGS -t

		:0
		* !To:[email protected]
		[email protected]
	}

------------------------------------------------------------------------------


Any idea what I'm doing wrong?

Thank you very much for your help.