Template select field not working correctly when templates in sub dir

[peterboorsma]

The template select field does not pick my selected template when the template.twig is stored in a sub directory of my theme folder.

Example:

My theme structure:

themename_folder

• templates_folder
  -- mytemplate_01.twig
  -- mytemplate_02.twig
  theme.yaml

In my theme.yaml:
template_directory: templates

My contenttype:

pages:
    name: Pages
    singular_name: Page
    fields:
        slug:
            type: slug
            uses: title
            group: content
        title:
            type: text
        body:
            type: html
            height: 300px
            allowtwig: true
        template:
            type: templateselect
            #filter: '*.twig'
    record_template: mytemplate_01.twig

If I select mytemplate_02.twig in the backend editor it's correctly stored but not rendered. There is no error message available.
It looks like the path is incorrect.

---

Install type: Packaged distribution
Database: mysql 5.7.26 - 127.0.0.1 via TCP/IP
PHP version: 7.3.9
Symfony version: v5.1.8
Operating System: Darwin - 19.6.0
Assets version: 4.1.4