Why after setting proxy_set_header Connection "Upgrade"; Do all response headers disappear from Responce?

Question

Nginx

1) Why after installing proxy_set_header Connection "Upgrade"; all response headers disappear from Responce ?
2) Is it possible to fix this without removing the Connection "Upgrade" (it is needed to work with websockets)?
Headers with Connection "Upgrade":

Headers without Connection "Upgrade":

Answer 1

Found the answer here:
https://stackoverflow.com/questions/15193743/nginx...