The enclosed content parameter will work differently when it is passed as a value to another shortcode. Making any change would be regressive I guess.
Ideally, $$enclosed_content$$ is meant for large content like HTML which you can’t pass via an attribute.
So I would suggest passing the value via attributes.
Also if possible you can restructure your shortcode content in a way that you are not passing shortcodes as value to another shortcode. Make sure you pass simple values strings, values from the post side. It is also easy to manage.
You could create multiple shortcodes where the nested shortcode in the content have different values passed.