Steps to reproduce the issue

Call $this->setDocumentTitle() from the HtmlView of a backend view with "site title display" (global configuration) to before or after page title.

Expected result

A nice page title that you set.

Actual result

"JPAGETITLE" as page title.

System information (as much as possible)

Additional comments

Since the JPAGETITLE language constant is not present in the backend but this function is inherited in the HtmlView it would be good to have it working also in the backend. It would need the missing language constant added.