[Dovecot] empty emails with 2.2.13/pigeonhole

[Cor Bosman]

I recently upgraded from 2.2.10 to 2.2.13, and also upgraded pigeonhole. Ever since im seeing some empty emails appear in my inbox.

Return-Path: <cricket at stats2.xs4all.net>
Delivered-To: <cor>
Received: from imapdirector1.xs4all.net ([194.109.26.173])
	by userimap9.xs4all.nl (Dovecot) with LMTP id CHu0MUDDjlOBdwAAwvsqNQ
	for <cor>; Wed, 04 Jun 2014 08:57:04 +0200

Thats all this mail contains. This only happens using LMTP/Sieve, and with many different senders/recipients. Debug log shows nothing out of the ordinary, except that the mail seems to be corrupted by the time it hits sieve. It's very hard to diagnose. Our path is kind of lengthy, and in theory it could happen everywhere.

Mail first arrives on incoming MX server which is sendmail. From there it's sent to a dovecot director using lmtp, which sends it to a server that does final delivery with sieve. Im not sure where the email gets corrupted. Any extra debugging I could turn on? 

Two extra things to note. So far it seems to only happen to emails that would have hit a matching sieve filter rule.  I have asked a dozen people to verify this, and all emails would have matched a filter if all was well. Instead, it gets dropped into the inbox because pigeonhole seems to be working with the corrupt file and cant match any rules anymore. And second, 99% of our email is handled differently, from the sendmail server directly into a local mailer, and that never causes issues. We're in the process of switching to lmtp.  

Any insights?

cor