Devise inline errors stop showing up when overriding update method

Using Rails 3.2, Devise 3.5.1, SimpleForm

I'm using a custom update method in Devise:

def update
    resource = resource_class.to_adapter.get!(send(:"current_#{resource_name}").to_key)
    resource_updated = update_resource(resource, account_update_params)
    if resource_updated
      sign_in resource_name, resource, :bypass => true
      redirect_to edit_member_registration_path, notice: "Updated successfully"
    else
      clean_up_passwords(resource)
      redirect_to edit_member_registration_path, alert: resource.errors.full_messages
    end
end

This is my form code:

<%= simple_form_for(resource, :as => resource_name, :url => registration_path(resource_name)) do |f| %>
  <%= f.error_notification %>
  <%= f.input :first_name %>
  <%= f.input :last_name %>
<% end %>

Everything works fine, but when there are validation errors, I can't figure out why they are only showing up in the Flash message and not inline.

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When I removed the custom update function, I get this behavior, which is exactly what I want:

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Is there something wrong with my update function?