gzip recompression on nginx in reverse proxy mode

[cw318]

Faced with strange behavior of nginx in reverse proxy mode. There is web
server 1 - the original source. web server 2 on nginx caching data in
reverse proxy mode between web server 1 and users.
Web server 1 delivers content in maximum gzip compression:
gzip compressed data, max compression, from Unix
Web server 2 delivers content not in maximum compression:
gzip compressed data, max speed, from Unix, original size modulo 2^32
328219
It looks like web server 2 recompresses gzip, but gzip compression is
disabled in the nginx config with the following directives:
    gzip_proxied off;
    gzip_static off;
    gzip off;
May be somebody has experienced similar behavior?
Expected behavior: delivery content to the client from cache that we get
from the original web server 1 (already in maximum compression)

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,294748,294748#msg-294748