proxy_ssl_certificate not working as expected

[elanh]

Here is my full "nginx -V" output:
nginx version: nginx/1.9.10
built by gcc 4.9.2 (Debian 4.9.2-10)
built with OpenSSL 1.0.1k 8 Jan 2015
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx
--conf-path=/etc/nginx/nginx.conf --error-log-path=/var/log/nginx/error.log
--http-log-path=/var/log/nginx/access.log --pid-path=/var/run/nginx.pid
--lock-path=/var/run/nginx.lock
--http-client-body-temp-path=/var/cache/nginx/client_temp
--http-proxy-temp-path=/var/cache/nginx/proxy_temp
--http-fastcgi-temp-path=/var/cache/nginx/fastcgi_temp
--http-uwsgi-temp-path=/var/cache/nginx/uwsgi_temp
--http-scgi-temp-path=/var/cache/nginx/scgi_temp --user=nginx --group=nginx
--with-http_ssl_module --with-http_realip_module --with-http_addition_module
--with-http_sub_module --with-http_dav_module --with-http_flv_module
--with-http_mp4_module --with-http_gunzip_module
--with-http_gzip_static_module --with-http_random_index_module
--with-http_secure_link_module --with-http_stub_status_module
--with-http_auth_request_module --with-threads --with-stream
--with-stream_ssl_module --with-http_slice_module --with-mail
--with-mail_ssl_module --with-file-aio --with-http_v2_module
--with-cc-opt='-g -O2 -fstack-protector-strong -Wformat
-Werror=format-security -Wp,-D_FORTIFY_SOURCE=2' --with-ld-opt='-Wl,-z,relro
-Wl,--as-needed' --with-ipv6

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,265281,265684#msg-265684