downcasting of values during field assignment

[skippy]

hello,

I'm noticing that if I assign an object that inherits from the ruby class which is created from the protocol definition, it is downcast, and I don't see any particular reason why. For example

Lets say I have the following classes. (The reason I'm doing this is I'm injecting a ton of validations into the new class; the other way to do this is to not have Corp::Location inherit from the proto-based ruby object but instead just serialize into it.... such as Corp::Location#to_proto calls Corp::WireDefinition::Location.new(self.to_hash).to_proto... thoughts on approach?)

Anyway, I digress a bit... check this out:

module Corp
  class Location < Corp::WireDefinition::Location
    #a ton of validations
  end
end

module Corp
  class Business < Corp::WireDefinition::Business
    # includes an array of Locations
  end
end

if I run the following, on assignment, the Corp::Location instance is downcast. This is problematic if I have methods within Corp::Location that I need to call later (such as running validations).

business = Corp::Business.new
business.locations = [Corp.Location.new, Corp.Location.new]
business.locations.first.is_a?(Corp.Location) # => false; it is a Corp::WireDefinition::Location

The culprit is this line: https://github.com/localshred/protobuf/blob/master/lib/protobuf/field/field_array.rb#L70

I don't understand why it is creating a new object here, downcasting it in the process, and git blame doesn't shed any light as to why this logic is here. Thoughts? Would it be ok if I submit a PR that rips this out?