Steps to reproduce:
1. Go to a site
2. Click Manage > Site pages
3. Click "Add page"
4. The pop-up shows a form to create a new page. It should be showing as well a select to choose the type of page (portlet, url, embedded, ...) but it does not.
That value is obviously wrong. I've been researching when this started happening and it was when the TagBuilder was introduced replacing the old implementation of the tag. So there might be other things broken because of this