I have auto-subscribe turned on, but I had to doveadm mailbox subscribe to a LDA/Sieve created mailbox today.

Did something break?

doveconf -n attached.

FreeBSD 
dovecot-2.3.9.3                Secure, fast and powerful IMAP and POP3 server
dovecot-pigeonhole-0.5.9_1     Sieve plugin for the Dovecot 'deliver' LDA and LMTP

--
Larry Rosenman                     http://www.lerctr.org/~ler
Phone: +1 214-642-9640 (c)     E-Mail: larryrtx@gmail.com
US Mail: 5708 Sabbia Dr, Round Rock, TX 78665-2106