imapc tries to fetch uid 0

[Nagy, Attila]

Hi,

This is a capture from an imapc client session (which is triggered by a 
message, received via LMTP):
* OK [CAPABILITY IMAP4rev1 NAMESPACE] Ready
2 LOGIN "uid" "pass"
2 OK LOGIN succeeded
1 LIST "" ""
* LIST (\Noselect) "/" ""
1 OK LIST completed
3 APPEND "INBOX" {568}
+ Ready for 568 octets of data
[...]
3 OK APPEND complete
4 EXAMINE "INBOX"
* FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
* OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft \*)] 
Flags permitted.
* 4 EXISTS
* 0 RECENT
* OK [UIDVALIDITY 1455885804]
* OK [UIDNEXT 5]
4 OK [READ-ONLY] EXAMINE successful
5 UID FETCH 0 (RFC822.SIZE BODY.PEEK[HEADER.FIELDS (Message-ID)])
5 BAD Illegal syntax: Bad message number 0

Dovecot 2.2.21

I don't see any problems with the conversation otherwise. Is it safe to 
assume this is a bug in imapc?