It seems that passing :only options to serializable_hash affects the serialization of :includes.

<pre>
person.serializable_hash(:include => :addresses)['addresses']
> "addresses"=>[

{"_id"=>"kudamm", "street"=>"Kudamm"}

,

{"_id"=>"tauentzienstr", "street"=>"Tauentzienstr"}

]

person.serializable_hash(:include => :addresses, :only => [:age, :blood_alcohol_content])['addresses']
>"addresses"=>[{}, {}]
</pre>

I've committed some failing specs:
https://github.com/njorden/mongoid/commit/0ceea8a4c4b3ace9d4892327ef228fe01df99154

I'm glad to investigate a solution, as long as I'm not missing something obvious or misunderstanding how this should be working. Any thoughts?

Thanks