Array inside a hash are not merged (array and nested hash merges properly)

I try to override a parameter on a host by adding an item to a list inside a hash but the list is not merged with the default value
"Merge overrides" and "Merge default" enabled on the class parameter, datatype hash

Default parameter value:

myUser:
  sshkeys:
    - publicKey1

I want to add a specific key on a host,
host override value:

myUser:
  sshkeys:
    - publicKey2

Value kept on the host:

myUser:
  sshkeys:
    - publicKey2

Expected value on the host:

myUser:
  sshkeys:
    - publicKey1
    - publicKey2