Package directory not found when using braces on filename

I’m trying to package django-tailwind, which uses cookiecutter templates (Jinja2) for generating file content as well as file and directory names. It fails to build when copying the package’s files, with this message:

copying src/tailwind/ -> build/lib/tailwind
copying src/tailwind/ -> build/lib/tailwind
error: package directory 'src/tailwind/app_template_v2/{{cookiecutter/app_name}}' does not exist

The path is actually src/tailwind/app_template_v2/{{cookiecutter.app_name}}, with a dot instead of a slash. The directory exists.

Could it be a bug that gets triggered when using such special chars on the filename? How can I work around it/fix it?

I’m using Nix 2.3.12, single user installation on Ubuntu 20.04.