Restrict activity modules feature does not work

Steps to reproduce
===============

1. Go to the admin -> variables page

2. At the bottom of the Permissions section, set
restrictmodulesfor to 'All Courses'
restrictbydefault to 'Yes'
defaultallowedmodules to some list that contains most but not all of the modules. For example select all of them except chat.

3. Save changes.

4. Start creating a new course. At the bottom of the create new course form, not that there is a 'Restrict activity modules?' bit, and that says 'Yes', and has the correct list of modules preselected.

5. Save changes.

6. Go to the new course. Turn editing on.

7. Attempt to add a chat.

Actual result
==========

The chat can be added.

Expected result
============

Chat should not even appear in the activity dropdowns.

Other points
==========

We have observed that this does not work on Postgres. We can't test in on MySQL.

We at the OU would really like to have this working in 1.6, if possible.