On another note, in the manifest.cfg I see no value in explicitly naming the theme path (e.g. ++theme.....):
development-css = ++theme++mycustomtheme/style.less
production-css = ++theme++mycustomtheme/style.css
Okaaaaaay!... updating this note.
There is great value since it's the only way to get the proper path to the theme's resources.
Be careful though, I've seen themes break because the path specifies a different theme name or a previous name, for example when the theme is copied, the only theme that dynamically renames these paths is the barceloneta theme.