collection_singular_ids not being set for Model has_many / belongs_to

First off this is a Rails 3.2 app using Ruby 2.1.3p242 and Mongo 1.7.1

I have a User model that has_many :host_clubs, :class_name => 'Club', :inverse_of => :host which has the following field field :host_club_ids since we are using Mongodb.

On the Club models side the relationship is as follows:

belongs_to :host, :class_name => 'User', :inverse_of => :host_club

When I create a club I can see the relationship is set by calling the following:

user.host_clubs => [#<Club _id: 568c02c7e30a9939cf00002c, ect ect...]

so it is returning the clubs associated, but when I try user.host_club_ids it returns => [].

I dont get any errors when creating the club but I cannot figure out why it wont set the host_club_ids field.

Here is the call used to create the club @club = @user.host_clubs.new(params[:club])

If anyone can point me in the right direction that would be great.