dovecot restart/stop&start fails due to child processes still running

stop dovecot && start dovecot randomly fails due to a running child process not exiting fast enough:

Oct 13 15:04:58 ubuntu dovecot: master: Error: service(anvil): Socket already exists: /var/run/dovecot/anvil
Oct 13 15:04:58 ubuntu dovecot: master: Error: service(anvil): Socket already exists: /var/run/dovecot/anvil-auth-penalty
Oct 13 15:04:58 ubuntu dovecot: master: Fatal: Failed to start listeners
Oct 13 15:04:58 ubuntu kernel: [11132.825253] init: dovecot main process (8668) terminated with status 89

The dovecot anvil process appears to be the cause of the problem:

root 8418 8080 0 15:02 pts/0 00:00:00 stop dovecot
root 8419 1 0 15:02 ? 00:00:00 dovecot/anvil
root 8422 8420 0 15:02 ? 00:00:00 grep dovecot

This is an issue specific to Ubuntu due to the use of upstart; upstart only monitors the parent process which exits before the child processes have completed; the original Debian init script appears to make provision for this and does not suffer from the same issue.

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: dovecot-common 1:2.0.13-1ubuntu3
ProcVersionSignature: Ubuntu 3.0.0-12.20-generic-pae 3.0.4
Uname: Linux 3.0.0-12-generic-pae i686
ApportVersion: 1.23-0ubuntu3
Architecture: i386
Date: Thu Oct 13 15:40:37 2011
InstallationMedia: Ubuntu-Server 11.10 "Oneiric Ocelot" - Release i386 (20111011)
ProcEnviron:
 LANGUAGE=en_GB:en
 PATH=(custom, no user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: dovecot
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.init.dovecot.conf: [deleted]