dsync panic

[Greg Rivers]

As per <http://wiki2.dovecot.org/Migration/Dsync>, I'm running the 
following command on a local dovecot server to replicate email for a 
single user from a remote IMAP server:

doveadm	-D \
 	-o imapc_host=remote.imap.server \
 	-o imapc_user=gcr \
 	-o imapc_password=XXXXXXXX \
 	-o imapc_list_prefix=IMAP \
 	-o imapc_features="rfc822.size fetch-headers" \
 	-o mail_prefetch_count=20 \
 	-o mail_fsync=never \
 	backup -R -u gcr imapc:

This runs fine for a while and successfully copies quite a lot of mail, 
but always aborts before completion with the following error:

dsync(gcr): Panic: file mail-transaction-log.c: line 271 
(mail_transaction_log_rotate): assertion failed: (file->locked)

The exit code is 262.  Does anyone know why this might happen or how to 
fix it?

-- 
Greg Rivers
-------------- next part --------------
# 2.2.15: /usr/local/etc/dovecot/dovecot.conf
# Pigeonhole version 0.4.6 (3e924b1b6c5c+)
# OS: FreeBSD 10.1-RELEASE-p6 amd64  
auth_verbose = yes
imap_id_log = *
imap_id_send = name * version * os * os-version *
mail_location = mdbox:~/.mdbox
mail_plugins = " quota zlib"
managesieve_notify_capability = mailto
managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date ihave duplicate editheader vnd.dovecot.debug imapflags notify vnd.dovecot.duplicate vnd.dovecot.pipe vnd.dovecot.filter vnd.dovecot.execute
namespace inbox {
  inbox = yes
  location = 
  mailbox Drafts {
    special_use = \Drafts
  }
  mailbox Junk {
    special_use = \Junk
  }
  mailbox Sent {
    special_use = \Sent
  }
  mailbox "Sent Messages" {
    special_use = \Sent
  }
  mailbox Trash {
    special_use = \Trash
  }
  prefix = 
}
passdb {
  args = %s
  driver = pam
}
plugin {
  sieve = file:~/sieve;active=~/.dovecot.sieve
  sieve_execute_bin_dir = /usr/local/etc/dovecot/sieve/execute
  sieve_execute_socket_dir = sieve-execute
  sieve_extensions = +notify +imapflags +editheader +vnd.dovecot.duplicate +vnd.dovecot.pipe +vnd.dovecot.filter +vnd.dovecot.execute +vnd.dovecot.debug
  sieve_filter_bin_dir = /usr/local/etc/dovecot/sieve/filter
  sieve_filter_socket_dir = sieve-filter
  sieve_global = /usr/local/etc/dovecot/sieve
  sieve_max_actions = 0
  sieve_max_redirects = 16
  sieve_max_script_size = 0
  sieve_pipe_bin_dir = /usr/local/etc/dovecot/sieve/pipe
  sieve_pipe_socket_dir = sieve-pipe
  sieve_plugins = sieve_extprograms
}
postmaster_address = postmaster at local.domain
protocols = imap lmtp sieve
quota_full_tempfail = yes
ssl_cert = </etc/ssl/certs/dovecot.pem
ssl_key = </etc/ssl/private/dovecot.pem
userdb {
  driver = passwd
}
verbose_proctitle = yes
protocol lmtp {
  mail_plugins = " quota zlib sieve"
}
protocol lda {
  mail_plugins = " quota zlib sieve"
}
protocol imap {
  mail_max_userip_connections = 250
  mail_plugins = " quota zlib imap_quota imap_zlib"
}