map_dom, map_sub issue

[Seri]

Hi, 

I have a map configuration as below

** haproxy configuratioin file
frontend http-in
  ...
  use_backend %[req.fhdr(host),lower,map_dom(/etc/haproxy/host_to_backend.map)]
  ...

backend www.a.com
  server www1 1.1.1.1:80

backend m.www.a.com
  server m.www1 2.2.2.2:80

** /etc/haproxy/host_to_backend.map file
www.a.com     www.a.coom
m.www.a.com  m.www.a.com

If I request "Host: www.a.com", www.a.com backend is chosen.
If I request "Host: m.www.a.com", ww.a.com backend not m.www.a.com backend is 
chosen.

Is this right behaviour?

Have I missed something?


Thanks,

Seri