Nginx with SSL maintaining appends domain name before request URL

Question

There is an Angular application in the dockerized Nginx. The Nginx configured for https mode with a trusted SSL certificate.
The Nginx config looks like:

worker_processes  1;

error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;

events {
    worker_connections  1024;
}

http {
    include       /etc/nginx/mime.types;
    default_type  application/octet-stream;

    log_format  trace  '$remote_addr - $remote_user [$time_local] "$request" '
    '$status $body_bytes_sent "$http_referer" '
    '"$http_user_agent" "$http_x_forwarded_for"';
    access_log  /var/log/nginx/access.log  main;
    sendfile        on;
    keepalive_timeout  65;

    gzip on;
    gzip_disable "msie6";

    gzip_comp_level 6;
    gzip_min_length 1100;
    gzip_buffers 16 8k;
    gzip_proxied any;
    gzip_types
      text/plain
      text/css
      text/js
      text/xml
      text/javascript
      application/javascript
      application/x-javascript
      application/json
      application/xml
      application/rss+xml
      image/svg+xml;

    ssl_session_cache   shared:SSL:10m;
    ssl_session_timeout 10m;

    server {
        server_name          www.example.com;
        ssl_certificate     /etc/ssl/example.crt;
        ssl_certificate_key /etc/ssl/example.key;
        listen               *:80;
        listen               *:443 ssl spdy;
        listen               [::]:80 ipv6only=on;
        listen               [::]:443 ssl spdy ipv6only=on;

        return 301 https://example.com$request_uri;
    }

    server {
        server_name          example.com;
        listen               *:80;
        listen               [::]:80;

        return 301 https://example.com$request_uri;
    }

    server {
        server_name         example.com;
        listen              *:443 ssl spdy;
        listen               [::]:443 ssl spdy;
        ssl_certificate     /etc/ssl/example.crt;
        ssl_certificate_key /etc/ssl/example.key;
        ssl_protocols       TLSv1 TLSv1.1 TLSv1.2;
        ssl_ciphers         HIGH:!aNULL:!MD5;
        keepalive_timeout   70;

        location / {
            root   /usr/share/nginx/html;
            index  index.html index.htm;
            try_files $uri $uri/ /index.html;
        }
    }
}

When the Angular app sends a rest request to the backend, like POST https://user-service/api/update/testuser, I see in the dev tools next request URL: POST https://example.com/user-service/api/update/testuser and get the 405 HTTP code in the response.
Such an issue isn't observed when the Nginx configured for only HTTP mode and the request URL in the dev tools is the same as defined in the Angular app e.g. POST http://user-service/api/update/testuser.
Perhaps this behavior somehow related to security policy, but I didn't find any settings and explanations in the Nginx documentation.

Additional information:
There are several dockerized services in one internal docker network among which the already mentioned Nginx with the Angular app. And only for the Nginx, there is opened port (port mapping). All other services are should be closed from the outside world, therefore, options for proxying requests are not considered.