When trying to create a new class with the option of XML export checked, this option isn't saved.

Steps to reproduce

1. Log in as admin in admin interface
2. Click “Setup”
2. Click left menu on “Classes”
3. Click “Content” link
4. Click “New class” button, at the bottom of the page

Name: The Class
Identifier: the_class
Class available for XML export: checked

6. Click “Add attribute” button, at the bottom of the page, with the type “Text line”

Name: The Attribute
Identifier: the_attribute
Available for XML export: checked

7. Click “OK” button