I'm using Rails 4.0.8, Ruby 2.1.2 and Mongoid 4.0.0 with Mongodb 2.6.3.<br />
Let's assume I have the following Mongoid::Criteria that is using a default scope which sorts the documents:

tracks = Track.where(:max_speed.gt => 60)
=> #<Mongoid::Criteria
  selector: {"max_speed"=>{"$gt"=>60}}
  options:  {:sort=>{"start_time"=>-1}}
  class:    Track
  embedded: false>

Calling reorder on tracks returns a criteria without sorting options, which is what I would have expected:

tracks.reorder
=> #<Mongoid::Criteria
  selector: {"max_speed"=>{"$gt"=>60}}
  options:  {}
  class:    Track
  embedded: false>

The problem is that reorder not only returns a criteria without ordering options, but also modifies the original tracks variable by removing the sorting options:

tracks
=> #<Mongoid::Criteria
  selector: {"max_speed"=>{"$gt"=>60}}
  options:  {}
  class:    Track
  embedded: false>

So reorder behaves more like a reorder! function if I understand it correctly. I know that I can use tracks.apply_default_scope to restore the original sorting options, but that feels like an unnecessary extra step.<br />
The unscoped method behaves just the way I would expect it: it returns an unscoped criteria, but does not change the variable it is being called on.

tracks = Track.where(user_id: "some_id")
=> #<Mongoid::Criteria
  selector: {"user_id"=>"some_id"}
  options:  {:sort=>{"start_time"=>-1}}
  class:    Track
  embedded: false>

tracks.unscoped
=> #<Mongoid::Criteria
  selector: {}
  options:  {}
  class:    Track
  embedded: false>

tracks
=> #<Mongoid::Criteria
  selector: {"user_id"=>"some_id"}
  options:  {:sort=>{"start_time"=>-1}}
  class:    Track
  embedded: false>

So is modifying the original variable really the intended behaviour of the reorder method?

Regards,
Carsten