Why does embedding KeyCloak into a another stack using requirements.yaml fail?

I ran into a really weird issue when using https://github.com/codecentric/helm-charts/tree/master/charts/keycloak to set up keycloak on k8s:

Using this helmchart and setting it up directly works pretty well, extraVolumes / mountPoints are processed as expected:

keycloak:
  enabled: true
  extraVolumeMounts: |
     - name: providers
       mountPath: /opt/jboss/keycloak/standalone/deployments/
  
   extraVolumes: |
     - name: providers 

However, embedding this in another stack via requirements.yaml with

- name: keycloak
  condition: keycloak.enabled
  version: 8.2.2
  repository: https://codecentric.github.io/helm-charts
  tag: 9.6

fails. The respective values for the new stack contains this:

keycloak:
  enabled: true
  replicaCount: 1

  ## Add additional volumes and mounts, e. g. for custom themes
  extraVolumeMounts: |
    - name: providers
      mountPath: /opt/jboss/keycloak/standalone/deployments/
  
  extraVolumes: |
    - name: providers

but the volume is not mounted properly, not getting any error either. The exact same values result in different deployments.

Is there anything wrong with the nested structure to provide the values for a requirement chart?

keycloak:
  keycloak:
    [content goes here]