We are using following config to place assetic results to a web/subdir.

framework:
  templating:
    assets_base_paths: "/subdir"

assetic:
    read_from:      "%kernel.root_dir%/../web/subdir"
    write_to:       "%kernel.root_dir%/../web/subdir"

It works for Symfony 2.6 but broken for Symfony >=2.7 with error:

[Symfony\Component\Asset\Exception\InvalidArgumentException]
"/subdir" is not a valid URL

thrown during container initialization.

Is this a BC break or did we miss something?