Last two changes should fix this:
Not yet -- this may be unrelated(?) but here is what I have after installing the newest source package:
Error: Couldn't load required plugin /usr/local/lib/dovecot/lib90_sieve_plugin.so: dlopen() failed: /usr/local/lib/dovecot/lib90_sieve_plugin.so: undefined symbol: mail_deliver_ctx_get_log_var_expand_table
Oh i guessing this requires the newest Dovecot source too (maybe you should put notice on the wiki that extprograms run-via-socket is broken until a new release?)
After installed newest Dovecot and Sieve, I getting this:
dovecot: lmtp(test@example.com): Debug: auth input: dovecot: lmtp(testl@example.com): Fatal: master: service(lmtp): child 7033 killed with signal 11 (core dumps disabled)
With set mail_debug=yes doesn't give anything else of interesting for this.