disable pool member with an irule

[root@iris:Active] config  b virtual bar list
virtual bar {
   snat automap
   pool foo
   destination 172.28.17.33:http
   ip protocol tcp
   rules myrule
   profiles {
      http {}
      tcp {}
   }
}
[root@iris:Active] config  b rule myrule list
rule myrule {
   when HTTP_REQUEST {
   if {[scan [HTTP::uri] "/down/%s" server] == 1} {
      LB::down pool foo member $server 80
      log local0. "URI: [HTTP::uri] MATCHED. server=$server"
  }
}
}

[root@iris:Active] config  curl -I http://172.28.17.33/down/10.10.70.110
curl: (52) Empty reply from server

[root@iris:Active] config  cat /var/log/ltm
Oct 26 21:28:09 local/iris notice mcpd[2926]: 01070638:5: Pool member 10.10.70.110:80 monitor status iRule down.
Oct 26 21:28:09 local/tmm err tmm[4672]: 01010028:3: No members available for pool foo
Oct 26 21:28:09 local/tmm info tmm[4672]: Rule myrule : URI: /down/10.10.70.110 MATCHED. server=10.10.70.110