Simple environment variable usage not working for me

here is my simple listen section of the haproxy config file:

listen graph_front
   bind *:8182
   mode tcp
   server graph_server graph.server.com:8182

this works just fine, but I need the address and port to be a environment variable. So I changed it to this:

listen graph_front
   bind *:8182
   mode tcp
   server graph_server "$GRAPH_ADDRESS":"$GRAPH_PORT"

the haproxy server restarts just fine, but it no longer forwards to the address in the environment variables.

any ideas?

For the record, this was diagnosed on the mailing list:
https://www.mail-archive.com/haproxy@formilux.org/msg30755.html