fixes #804

app/models/tag.rb

@@ -87,6 +87,7 @@ class Tag < ActiveRecord::Base
     def update_category_cache_for_all(force = false)
       if category_changed? || force
         update_category_cache
+        update_category_post_counts if category_changed?
         
         Danbooru.config.other_server_hosts.each do |host|
           delay(:queue => host).update_category_cache
@@ -94,6 +95,12 @@ class Tag < ActiveRecord::Base
       end
     end
     
+    def update_category_post_counts
+      old_field = "tag_count_#{Danbooru.config.reverse_tag_category_mapping[category_was]}".downcase
+      new_field = "tag_count_#{category_name}".downcase
+      Post.raw_tag_match(name).update_all("#{old_field} = #{old_field} - 1, #{new_field} = #{new_field} + 1")
+    end
+    
     def update_category_cache
       Cache.put("tc:#{Cache.sanitize(name)}", category, 1.hour)
     end