Inconsistent method_defined? behaviour

Attribute methods of ActiveRecord classes are created via method_missing but take care only for handling respond_to? properly.
For example method_defined? or instance_methods know nothing about methods dynamically created by AR.

$ script/generate model User login:text
$ script/console
>> User.method_defined?(:login)
=> false
>> User.instance_methods.include?('login')
=> false
>> User.new
=> Userid: integer....
>> User.method_defined?(:login)
=> true
>> User.instance_methods.include?('login')
=> true

This isn't supposed to be a problem with more 'magic' methods like dynamic finders. At least dynamic finder methods keep consistent behavior and are always reported as non-existed.
Issue touches ActiveRecord 3.0 as well.