selenium test fails when render nothing: true

I have the following action that is rendered using ajax in my controller:

def save_something
  User.create(:attr1 => params[:attr1], :attr2 => params[:attr2]
  render nothing: true
end

This works fine when tested in the browser but my selenium tests (:js => true) fail. When I check the test log the error is as follows:

AbstractController::ActionNotFound - The action 'show' could not be found for Resource::UsersController:

Are there issues with render nothing: true when rendering ajax responses?