dovecot hung after executing UID COPY

Issue

• dovecot hung after executing UID COPY against a non-existent mailbox.

# nc localhost 143
    * OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE STARTTLS AUTH=PLAIN] Dovecot ready.
    1 LOGIN testuser testuser
    1 OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS MULTIAPPEND UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS] Logged in
    2 SELECT INBOX
    * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
    * OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft \*)] Flags permitted.
    * 3 EXISTS
    * 0 RECENT
    * OK [UNSEEN 3] First unseen.
    * OK [UIDVALIDITY 1406525494] UIDs valid
    * OK [UIDNEXT 4] Predicted next UID
    * OK [HIGHESTMODSEQ 1] Highest
    2 OK [READ-WRITE] Select completed.
    3 UID COPY 5 hoge
    3 NO [TRYCREATE] Mailbox doesn't exist: hoge
    4 SELECT INBOX

    ******    dovecot doesn't response to SELECT command    ******