page-user-register.tpl.php not overridden

I'm trying to customize the user registration page in a zen subtheme.
The template candidates files suggested by themer devel are page-user.tpl.php and page-user-register.tpl.php, but when I try to create them, page.tpl.php (placed in the subtheme as well) is not overridden.
All other pages are working fine.
I've clean theme registry and checked all file permissions, I still can't get this.
What did I miss?

Thanks