Special:NewPages ignores parameters set in the URL, particularly, username, whether submitted by form or manually, in the address bar.
In /includes/specials/SpecialNewpages.php SpecialNewpages::$opts have NULL values for all options; they are never filled.
The issue arose after upgrade to MW 1.25.1 from 1.24.2; maintenance/update.php has been run. The PHP engine is HHVM 3.7.1.
Nothing really useful in debug info except the fact that the query parametres never get set.