[Dovecot] multiple Return-Path headers added using lmtp director

Emails arrive with 2 Return-Paths when using lmtp director. Is this something configurable in the director or is this a bug?

Return-Path: xxxxxx@xs4all.net Delivered-To: Received: from lmtpdirector1.xs4all.net ([194.109.26.176]) by lmtp2.xs4all.net (Dovecot) with LMTP id gOe2E3YSkE/aEAAAYH/+MA for ; Thu, 19 Apr 2012 15:26:14 +0200 Return-Path: xxxxxxxxx@xs4all.net Received: from mxdrop-builder.xs4all.nl ([194.109.23.200]) by lmtpdirector1.xs4all.net (Dovecot) with LMTP id CnOvKTkzjU9sJQAAbddgHA ; Thu, 19 Apr 2012 15:26:14 +0200

Regards