activeresource xml/json encoding inconsistency

the activeresource encoding for xml/json seem to be inconsistent: xml will incude the element name as root

from activeresource/base.rb

self.class.format.encode(attributes, {:root => self.class.element_name})

whereas json will use

self.class.format.encode(attributes, options)

so when an activeresource gets saved, the decoded parameters (on the REST API side) are different, e.g.

{"city"=>nil, "name"=>"Foo Bar" }   (JSON) vs.
{"person" => { "city=>nil, "name"=> "Foo Bar" } } (XML)

so when using json, i can't just use Person.find().update_attributes(params[:person]) in my controller.

is this intentional? looks like a bug.