Calling delete on a has_many :through association does not call destroy on the association object

Here is an example:

class GroupContentAssignment < ActiveRecord::Base
  belongs_to :group
  belongs_to :content, :counter_cache => true
  
  has_many :annotations, :dependent => :destroy
end

class Group < ActiveRecord::Base
  has_many :group_content_assignments, :dependent => :destroy
  has_many :assigned_contents, :through => :group_content_assignments
end

class Content < ActiveRecord::Base
  has_many :group_content_assignments, :dependent => :destroy
end

If I do the following...

group = Group.first
content = Content.first
group.assigned_contents << content

... an instance of GroupContentAssignment is created and saved and the counter_cache field on Content is incremented. But when removing...

group.assigned_contents.delete content

... no call to the destroy method of GroupContentAssignment is made and so destroy is not called for all its annotations and the counter_cache of the belonging Content is not decremented.

See also: #1196, http://railsforum.com/viewtopic....