When I enter any form within this bundle (either block form or page form) bundle tries to load its JS resources using invalid URL:

Page at:
http://localhost:8080/app_dev.php/admin/pages/new

Requested resources (with 404 error):
http://localhost:8080/bundles/_themes/[theme_name]/default/bitbagsyliuscmsplugin/js/bitbag-page-slug.js
http://localhost:8080/bundles/_themes/[theme_name]/default/bitbagsyliuscmsplugin/js/bitbag-page-slug.js

Page at:
http://localhost:8080/app_dev.php/admin/blocks/new/image

Requested resources (with 404 error):
http://localhost:8080/bundles/_themes/[theme_name]/default/bitbagsyliuscmsplugin/js/bitbag-block-image-preview.js
http://localhost:8080/bundles/_themes/[theme_name]/default/bitbagsyliuscmsplugin/js/bitbag-block-image-preview.js

Yep, both are requested twice lol. The base path for the resources should be: /bundles. This is my directory structure:

I'm using:

        "php": "^7.1",
        "bitbag/cms-plugin": "^1.3",
        "sylius/sylius": "1.2.*",
        "symfony/symfony": "^3.4|^4.1"