Incorrect diff for a string

Hi, i've got two json files:

old.json

{
  "network": {
    "domain": "old.domain"
  }
}

new.json

{
  "network": {
    "domain": "new.domain"
  }
}

When i run:

jsondiff.diff(old_json, new_json, syntax="symmetric")

I've got this:

{
    "network": {
        "domain": [
            "old.domain",
            "new.domain"
        ]
    }
}

Instead of:

{
    "network": {
        "domain": {
            "$delete": [ "old.domain" ],
            "$insert": [ "new.domain" ]
        }
    }
}

The json expected that I've written is probably not right, it's just an example to show the diff keys I expect.

It is normal behavior? Did I forget something?

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