Support multiple directories with same package-ecosystem

We're using the composer-bin-plugin to separate some CI tools from our own dependencies:

# .gitlab/dependabot.yml

version: 2
updates:

  # composer.json
  - package-ecosystem: "composer"
    directory: "/"
    schedule:
      interval: "daily"
    commit-message:
      prefix: "deps(php)"
    open-pull-requests-limit: 10

  # vendor-bin/phpcs/composer.json
  - package-ecosystem: "composer"
    directory: "/vendor-bin/phpcs/"
    schedule:
      interval: "daily"
    commit-message:
      prefix: "deps(php)"
    open-pull-requests-limit: 10

  # vendor-bin/php-cs-fixer/composer.json
  - package-ecosystem: "composer"
    directory: "/vendor-bin/php-cs-fixer/"
    schedule:
      interval: "daily"
    commit-message:
      prefix: "deps(php)"
    open-pull-requests-limit: 10

  # vendor-bin/psalm/composer.json
  - package-ecosystem: "composer"
    directory: "/vendor-bin/psalm/"
    schedule:
      interval: "daily"
    commit-message:
      prefix: "deps(php)"
    open-pull-requests-limit: 10

However, Dependabot-GitLab only seems to handle the first of these entries (we're using dependabot-standalone 0.9.7).

Am I doing something wrong or is this a limitation of dependabot or dependabot-gitlab?

PS: Monorepos probably have the same issue.