Why is password type of AzureKeyVaultSecret dropped when creating LinkedService via powershell,

Question

I'm attemping to create a LinkedService via the powershell command

New-AzureRmDataFactoryV2LinkedService -ResourceGroupName rg -DataFactoryName df -Name n -DefinitionFile n.json 

the result is that the LinkedService is created, however the reference to the password type of AzureKeyVaultSecret is removed rendering it non-operational

The config file n.json was extracted from the DataFactory code tab and has the syntax below...

{
"name": "<name>",
"type": "Microsoft.DataFactory/factories/linkedservices",
"properties": {
    "type": "Oracle",
    "typeProperties": {
        "connectionString": "host=<host>;port=<port>;serviceName=<serviceName>;user id=<user_id>",
        "password": {
            "type": "AzureKeyVaultSecret",
            "store": {
                "referenceName": "Prod_KeyVault",
                "type": "LinkedServiceReference"
            },
            "secretName": "<secretname>"
        }
    },
    "connectVia": {
        "referenceName": "<runtimename>",
        "type": "IntegrationRuntimeReference"
    }
}

}

When the new LinkedService is created, the code looks exactly the same except properties->typeProperties->password is removed and requires manual configuration - which I'm trying to avoid if possible.

Any thoughts?