[Dovecot] dsync/imapc migration question

[Gedalya]

Doing an imapc migration with the pop3 migration plugin, using doveadm 
backup -R.

I occasionally get the following output:

dsync(user at domain.tld): Error: imapc(mail01.domain.tld:143): Server 
disconnected unexpectedly
dsync(user at domain.tld): Error: imapc(mail01.domain.tld:143): Server 
disconnected unexpectedly
dsync(user at domain.tld): Error: imapc(mail01.domain.tld:143): Server 
disconnected unexpectedly
dsync(user at domain.tld): Warning: I/O leak: 0xb7648650 (line 1229, fd 10)
dsync(user at domain.tld): Warning: I/O leak: 0xb7648650 (line 1229, fd 11)
dsync(user at domain.tld): Warning: Timeout leak: 0xb76488b0 (line 1316)
dsync(user at domain.tld): Warning: Timeout leak: 0xb76488b0 (line 1316)

The source server is really crappy, no need to look at the dovecot side 
for causes. My question is: is it possible that the migration did 
complete successfully? Dovecot does seem to continue and it's kind of 
vague on what went wrong, and did it re-try. This operation can take 
several hours on large mailboxes so this question is really meaningful 
in my case. (I'd try with -D but it's really hard to reproduce this on 
demand).

Thanks

Gedalya