Forum: Ruby on Rails action_mailer.default_url_options not used in named routes within mailer view ?

In my mailer view I have a named route :

accept_user_invitation_url(@resource, :invitation_token =>
@resource.invitation_token)

In my routes :
accept_user_invitation  GET    /users/invitation/accept(.:format)
{:action=>"edit", :controller=>"users/invitations"}

in development , I set
config.action_mailer.default_url_options = { :host => 'lvh.me' , :port
=> 3000}

====

I am generating a mail  from a subdomain form,
http://foo.lvh.me:3000/users/invitation/new  ( submit to   POST
http://foo.lvh.me:3000/users/invitation/create)

in the mailer view the accept_user_invitation_url is NOT using the
config.action_mailer.default_url_options
but rather  generating the url with the current subdomain host
http://foo.lvh.me:3000

however with a ddebugger in mailer, before rendering , the default is
still correct....
Rails.configuration.action_mailer.default_url_options =>
{:host=>"lvh.me", :port=>3000}
why the named route is not using it ?