Due to the initialisation of fields in "create page" dialog, template availability is not working correctly allowing users to create subpages of templates which shouldn't be available.

Steps to reproduce in travel demo:

1. Create a template availability rule for pur template. For example, restricting its access to superuser role 
2. Access admin central with an user other than superuser. For example Eric (Editor) and create a new page from the root: public users template is not available as configured in step 1
3. Now create a new subpage from /travel/members/protected: public users template is selected by default as it is the parent's template, and therefore, it is possible to create a page with this template.