Problem with counter cache in many-to-many relationship

Hi guys,
I am having trouble getting to counter cache to work properly with a
many-to-many relationship. What I have done is:

rails g scaffold post title:string body:text
rails g scaffold tag name:string taggings_count:integer
rails g model tagging post_id:integer tag_id:integer

Then I created the relationship as shown in my Gist:

The idea is to have an input field when creating a post, where tags can
entered seperated by comma. The tag_names method then splits those tags,
adds new ones and deletes the ones that are now missing.

The counter_cache is correctly increased when adding a tag to the list.
However, decreasing the number after a tag removal does not work.

I have done some searching and found several blog articles (e.g.
explaining that this was a bug in Rails 3.0.x that has been addressed in
edge rails. See the old bug report on lighthouse:
then the fix on Github:
Correctly update counter caches on deletion for has_many :through [#2… · rails/rails@52f09ea · GitHub

Why am I still having this problem, when it was fixed two years ago? Am
missing something here?


rails -v

Rails 3.2.8