Hello,
this is possible too late but may useful

I have'nt found any solution
and just recompiled the Nginx with a little patch

i've changed file ./src/http/ngx_http_request.c

in function ngx_http_create_request:

r->http_version = NGX_HTTP_VERSION_10

to

r->http_version = NGX_HTTP_VERSION_9

this may ugly but now working as expected