dovecot - Aug 2015 - Error when reading attachment - one byte overhead?

After converting maildir to mdbox mail periodically obtained these messages:

Aug 13 11:22:27 mailsrv dovecot: imap(user-aaa): Error: 
read(/usr/share/smbusers/user-aaa/mail/attachments/a0/8e/a08e3e63e11aae3f37020bdca0da7d-7b39ab07ea73ba559d450000dec08558[base64:18
b/l]) failed: Stream is larger than expected (434427 > 434426, eof=1)
Aug 13 11:22:27 mailsrv dovecot: imap(user-aaa): Error: 
read(attachments-connector(/usr/share/smbusers/user-aaa/mail/storage/m.23)) 
failed: 
read(/usr/share/smbusers/user-aaa/mail/attachments/a0/8e/a08e3e63e11aae3f37020bdca0da7d-7b39ab07ea73ba559d450000dec08558[base64:18
b/l]) failed: Stream is larger than expected (434427 > 434426, eof=1) 
(FETCH BODY[] for mailbox ?????? ????????/??? ?????? UID 20)
Aug 13 11:22:27 mailsrv dovecot: imap(user-aaa): Disconnected: FETCH 
read() failed in=16923 out=497431

How to correct it? Conversion was did with 2.2.8 version, next will 
installed 2.2.18.

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