App ViewModels not found when routing to a Module

I had a ViewModel `class View_Newsletter extends \ViewModel` at `fuel/app/classes/view/newsletter.php` which worked fine when accessing a page served by a Controller in app.

When I then accessed a page within a Module the ViewModel could no longer be found, reporting the error `OutOfBoundsException [ Error ]: ViewModel "View_Newsletter" could not be found`