Ruby on Rails

I'm trying to use an array column to crete an association between 2 models. I remember that in the past this was working, but I think something has changed and now it's not working anymore. Here is the deal:

Ruby 2.4.3p205 (2017-12-14 revision 61247) [x86_64-linux]

Rails 5.1.5

app/models/user.rb

# Having the columns id, name, email
class User < ApplicationRecord
end

app/models/group.rb

# Having the columns id, name, user_ids[]
class Group < ApplicationRecord
  has_many :users, primary_key: :user_ids, foreign_key: :id
end

And the oddest thing about this is that the following works fine:

Group.first.users

It gives me the list of the users with the ids filled on that field, but the following doesn't work:

Group.first.users.load

It gives me an empty list. And, since the load method doesn't work, I cannot do any operation like #each or #to_a.

I already did some dig up, and found the source of the problem here:
https://github.com/rails/rails/blob/v5.1.5/activerecord/lib/active_record/associations/association_scope.rb#L79

The first command don't replace the original value by a Replaceable, the second does. Maybe we just need a ReplaceableArray or something like that, or I'm missing something here.

Can anyone help me with that?