When upgrading to rails 4 and trying to modify tags via the tag_list method i get the following:
WARNING: Can't mass-assign protected attributes for ActsAsTaggableOn::Tagging: tag_id, context, taggable
I got rid of the protected attributes gem and it worked fine.
I monkeypatched ActsAsTaggableOn::Tag and ActsAsTaggableOn::Tagging so they are attr_accessibles
You want to include a gist of the work you did? Would probably also be useful to submit a PR with it.
$ cat config/initializers/acts_as_taggable_on_patch.rb
attr_accessible :tag_id, :context, :taggable
Starting with acts-as-taggable-on 4.0.0, Tagging needs :tag on the list of attributes to make accessible as well.