FIX: changing category within edit grace period as TL3 pops up an error

app/controllers/topics_controller.rb

@@ -130,7 +130,7 @@ class TopicsController < ApplicationController
 
     if changes.length > 0
       first_post = topic.ordered_posts.first
-      success = PostRevisor.new(first_post, topic).revise!(current_user, changes)
+      success = PostRevisor.new(first_post, topic).revise!(current_user, changes, skip_validations: true)
     end
 
     # this is used to return the title to the client as it may have been changed by "TextCleaner"