Hi, after upgrading Mongoid to 8.1, eager-loading doesn't work for me in this case:

 
class Channel
  belongs_to :organization
end
class ManagerChannel < Channel; end
 
Channel.includes(:organization).map(&:organization) # works
Channel.where(_type: 'ManagerChannel').includes(:organization).map(&:organization) # works
ManagerChannel.includes(:organization).map(&:organization) # doesn't work (n+1 queries)
 
I have another model with the same behavior.
I'm on 8.1.8, but can reproduce it on 8.0.1 too.