TYPO3 Core

When using the following scenario:

A site package site set depends on another site set which defines a settings.definition.yaml file. In this settings.definition.file there are two settings, both are readonly. Additionally, the site package site set defines also a settings.definition.yaml file which also only readonly settings:

EXT:site
  dependencies:
    - my-vendor/some-ext
  settings.definitions.yaml:
    settings:
        site.some_setting:
        label: "Some setting" 
        type: "string" 
        readonly: "true" 
        default: "Some value" 

EXT:some_ext
  settings.definitions.yaml:
    settings:
        some_set.some_setting:
        label: "Some setting" 
        type: "string" 
        readonly: "true" 
        default: "Some value" 

This results in the following error in the backend (Site Management > Settings):

This site depends on invalid site sets
Site set 'my-vendor/site' is disabled: Missing dependency 'my-vendor/some-ext'

I would expect that the settings of some-ext are displayed correctly (as readonly) - apart from that the error message is misleading. This also happens when only one setting is defined as readonly and the others are writable.

If I remove the settings.definitions.yaml from some_ext, everything works, the readonly settings are correctly displayed readonly.

Background: I would like to use the settings definitions as a central place to define values (like with TypoScript constants previously), but they must not be overridden via the GUI.