How to map multiple AWS LoadBalancer ports to a single instance port

I have setup like this — Two ports on my load balancer map to a single port on my instance (the instance checks the HTTP header and issues a HTTP redirect to the HTTPS site for any non HTTPS request). The AWS dashboard shows:

LB Proto| LB Port| Inst Proto| Inst Port| SSL Cert
---------------------------------------------------
HTTP    | 80     | HTTP      | 8080     | N/A   
HTTPS   | 443    | HTTP      | 8080     | my_ssl_cert 

On my instance, I can inspect the incoming traffic as follows:

sudo ngrep -q -d eth0 -W byline port 8080

This succeeds: (https to the load balancer)

curl -k https://111.111.111.111/

but this fails: (http to the load balancer)

curl     http://111.111.111.111/

(where 111.111.111.111 is the loadbalancer's IP)

Curl stalls and times out, and I never see activity on port 8080 on my instance with ngrep (I do when I send the first request).

What's up? How come my loadbalancer isn't forwarding ANY traffic received on port 80 to port 8080 on my instance?