API allows to set default template for an operating system (POST /api/operatingsystems/:operatingsystem_id/os_default_templates) without prior association of the template with the os (PUT /api/operatingsystems/:id). It successfully sets the default template, but gets the OS to inconsistent stata UI isn't prepared for. OS detail page then displays a message that "No templates were found" and renders empty dropdown for template kind of the default template (see the attached screenshot).

Setting a default template should automatically associate the template with the OS. It doesn't make sense for the API to keep this operation in two steps.