Nginx filter policy is not working as expected when using content-caching

master_process off;
worker_processes  1;
daemon off;
error_log /dev/stdout debug;

events {
  accept_mutex off;
  worker_connections 5000;
}



http {
    proxy_cache_path /tmp/cache levels=1:2 keys_zone=apicast_cache:10m;

    upstream backend {
        server 127.0.0.1:8081;
        balancer_by_lua_block {
          ngx.log(ngx.ERR, "Setting header on balancer")
          ngx.req.set_header("if-match", "anything")
        }
        keepalive 10;  # connection pool
    }

    server {
        access_log  off;
        listen 8081;
        resolver 8.8.8.8;

        location / {
          rewrite_by_lua_block {
            local h = ngx.req.get_headers()
            ngx.req.clear_header("if-match")
            ngx.say(require("cjson").encode(h))
          }
        }
    }

    server {

      access_log  off;
      listen 8080;
      resolver 8.8.8.8;

      location / {

          rewrite_by_lua_block {
            ngx.req.clear_header("if-match")
          }

          content_by_lua_block {
             ngx.exec("@upstream")
          }
      }

      location @upstream {

        set $cache_request 'false';
        set $cache_zone 'off';

        proxy_cache apicast_cache;
        proxy_cache_key $scheme$request_method$proxy_host$request_uri;
        proxy_no_cache "false";
        proxy_cache_valid 200 302 1m;

        add_header X-Cache-Status $upstream_cache_status;

        proxy_pass http://backend;
        proxy_http_version 1.1;
      }
    }
}

(gdb) bt
#0  ngx_http_not_modified_header_filter (r=0x55c21900e990) at src/http/modules/ngx_http_not_modified_filter_module.c:71
#1  ngx_http_not_modified_header_filter (r=0x55c21900e990) at src/http/modules/ngx_http_not_modified_filter_module.c:55
#2  0x000055c216ff8069 in ngx_http_lua_send_header_if_needed (ctx=0x55c21900f780, r=<optimized out>) at ../ngx_lua-0.10.19/src/ngx_http_lua_util.c:549
#3  ngx_http_lua_send_header_if_needed (r=<optimized out>, ctx=<optimized out>) at ../ngx_lua-0.10.19/src/ngx_http_lua_util.c:524
#4  0x000055c216ff80e8 in ngx_http_lua_send_chain_link (r=r@entry=0x55c21900e990, ctx=ctx@entry=0x55c21900f780, in=in@entry=0x55c21900fd40)
    at ../ngx_lua-0.10.19/src/ngx_http_lua_util.c:591
#5  0x000055c216ff8327 in ngx_http_lua_send_chain_link (r=r@entry=0x55c21900e990, ctx=ctx@entry=0x55c21900f780, in=in@entry=0x55c21900fd40)
    at ../ngx_lua-0.10.19/src/ngx_http_lua_util.c:569
#6  0x000055c216fec479 in ngx_http_lua_ngx_echo (L=0x7f4f3d2a7ab0, newline=<optimized out>) at ../ngx_lua-0.10.19/src/ngx_http_lua_output.c:239
#7  0x00007f4f3d726f75 in lj_BC_FUNCC () from /usr/local/openresty/luajit/lib/libluajit-5.1.so.2
#8  0x000055c216ff9a52 in ngx_http_lua_run_thread (L=L@entry=0x7f4f3d2d0380, r=r@entry=0x55c21900e990, ctx=ctx@entry=0x55c21900f780, nrets=<optimized out>,
    nrets@entry=0) at ../ngx_lua-0.10.19/src/ngx_http_lua_util.c:1167
#9  0x000055c216ffd7a8 in ngx_http_lua_rewrite_by_chunk (L=0x7f4f3d2d0380, r=0x55c21900e990) at ../ngx_lua-0.10.19/src/ngx_http_lua_rewriteby.c:337
#10 0x000055c216ffd9ee in ngx_http_lua_rewrite_handler (r=0x55c21900e990) at ../ngx_lua-0.10.19/src/ngx_http_lua_rewriteby.c:162
#11 0x000055c216f48b9d in ngx_http_core_rewrite_phase (r=0x55c21900e990, ph=<optimized out>) at src/http/ngx_http_core_module.c:932
#12 0x000055c216f443e5 in ngx_http_core_run_phases (r=r@entry=0x55c21900e990) at src/http/ngx_http_core_module.c:878
#13 0x000055c216f444a4 in ngx_http_handler (r=r@entry=0x55c21900e990) at src/http/ngx_http_core_module.c:861
#14 0x000055c216f4f1c5 in ngx_http_process_request (r=r@entry=0x55c21900e990) at src/http/ngx_http_request.c:2081
#15 0x000055c216f4f747 in ngx_http_process_request_headers (rev=<optimized out>) at src/http/ngx_http_request.c:1483
#16 0x000055c216f4fb24 in ngx_http_process_request_line (rev=0x7f4f3c6fe200) at src/http/ngx_http_request.c:1154
#17 0x000055c216f35996 in ngx_epoll_process_events (cycle=<optimized out>, timer=<optimized out>, flags=<optimized out>) at src/event/modules/ngx_epoll_module.c:901
--Type <RET> for more, q to quit, c to continue without paging--z
#18 0x000055c216f2b966 in ngx_process_events_and_timers (cycle=cycle@entry=0x55c219009950) at src/event/ngx_event.c:257
#19 0x000055c216f34e68 in ngx_single_process_cycle (cycle=0x55c219009950) at src/os/unix/ngx_process_cycle.c:323
#20 0x000055c216f09e6d in main (argc=<optimized out>, argv=<optimized out>) at src/core/nginx.c:382
(gdb)

{
  "services": [
    {
      "id": 42,
      "backend_version": "1",
      "backend_authentication_type": "service_token",
      "backend_authentication_value": "token-value",
      "proxy": {
        "hosts": [
          "eloy",
          "one",
          "one.com"
        ],
        "api_backend": "https://echo-api.3scale.net",
        "proxy_rules": [
          {
            "pattern": "/",
            "http_method": "GET",
            "metric_system_name": "hits",
            "delta": 2
          },
          {
            "pattern": "/",
            "http_method": "POST",
            "metric_system_name": "hits",
            "delta": 2
          }
        ],
        "policy_chain": [
          {
            "name": "apicast.policy.nginx_filters",
            "configuration": {
              "headers": [
                {
                  "name": "If-Match",
                  "append": true
                }
              ]
            }
          },
          {
            "name": "content_caching",
            "version": "builtin",
            "configuration": {
              "rules": [
                {
                  "cache": true,
                  "header": "X-Cache-Status",
                  "condition": {
                    "combine_op": "and",
                    "operations": [
                      {
                        "left": "oo",
                        "op": "==",
                        "right": "oo"
                      }
                    ]
                  }
                }
              ]
            }
          },
          {
            "name": "apicast.policy.apicast"
          }
        ]
      }
    }
  ]
}