Why is the "readinessState" detail of /health different from the readiness probe status?

Question

In Spring-Boot 2.4, I have this problem with the Actuator health endpoint and readiness probe. When one of my custom key components is down, the /health/readiness endpoint says DOWN and the /health endpoint too, but the readinessState detail of /health still says UP.

Why is it that way? Shouldn't readinessState say DOWN too?

None of the many tutorials I found online seem to address this question.

My hypothesis: the readinessState has nothing to do with readiness and exposes another piece of information. I hope I'm wrong, because it would be nonesense and what I understand of the code seems to indicate otherwise.

---

More about my configuration:

Relevant excerpt from application.yml

management:
  endpoints:
    web:
      base-path: /
  endpoint:
    health:
      show-details: ALWAYS
      probes:
        enabled: true
      group:
        readiness:
          include: db, myCustom, diskSpace

And when I make myCustom go DOWN, following results appear:

GET /health

{
    "status": "DOWN",
    "components": {
        ...,  // other components
        "myCustom": {
            "status": "DOWN"
        },
        "readinessState": {
            "status": "UP"  // here UP
        }
    },
    "groups": [
        "liveness",
        "readiness"
    ]
}

GET /health/readiness

{
    "status": "DOWN",  // but here DOWN
    "components": {
        ...,  // other components
        "myCustom": {
            "status": "DOWN"
        }
    }
}