SERVFAIL when unbound forward-addr is an ssh forward port tunnel

[ronvarburg at yahoo.com]

 With

-------------------------------------------------------------
 server:
 directory: "/etc/unbound"
 do-daemonize: no
 tcp-upstream: yes
 trust-anchor-file: trusted-key.key
 use-syslog: yes
 username: "unbound"

 forward-zone:
 name: "."
 forward-addr: 127.0.0.1 at 1053
-------------------------------------------------------------

 and
 % ssh -L 127.0.0.1:1053:127.0.0.1:53 server
,
 % drill nameToQuery

returns SERVFAIL. In fact, any query doesn't work.
According to tcpdump -vv -x -X -s 1500 -i lo 'port 1053',
nothing being sent to the forward-addr.

While
 % drill -I 127.0.0.1 -p 1053 -4 -t nameToQuery

succeeds. Is that expected, for example because it is inherent to the NS protocol?
If it supposed to work, how to further debug it?