As per the design spec in packages/news/www/doc/design.html
Note that different package instances of the News application can be distinguished by the column 'package_id' (and not by the inherited context_id in acs_objects). We therefore need only a single cr_folder named 'news' to hold all news items.there is only one cr_folder holding all the news items. When the news items are created they get a context_id of the cr_folder. Since this folder is not associated with anything in particular, it has a context_id of -100. The problem with this is that permissions set on a mounted instance of news are meaningless, so you can't for instance grant general_comments_create to The Public on a mounted news app and have the permission bubble through.
Because I have only one mounted instance I changed the context_id of the cr_folder to the id of the mount instance - but I'm struggling to think of a generic solution without changing the one folder deign...
Any ideas anyone?