Modified_Time missing from Zoho CRM API Contacts, Products, and Custom Linking module response

Hi, I'm using the CRM API to GET Records method. For most of the modules the If-Modified-Since works fine and the API returns Modified_Time in the response.

However, I noticed for the these modules: Contacts, Products, and Custom Linking (Contact_x_Accounts), they don't return the Modified_Time field. For example, https://www.zohoapis.eu/crm/v2/Products, returns:

{
    "data": [
        {
            "Product_Category": null,
            "$approval": {
                "delegate": false,
                "approve": false,
                "reject": false,
                "resubmit": false
            },
            "Owner": {
                "name": "XXXXXX",
                "id": "XXXXXX",
                "email": "XXXXXX"
            },
            "$currency_symbol": "£",
            "$field_states": null,
            "$review_process": {
                "approve": false,
                "reject": false,
                "resubmit": false
            },
            "Product_Name": "XXXXXX,
            "$taxable": true,
            "$editable": true,
            "$orchestration": false,
            "$review": null,
            "$state": "save",
            "$process_flow": false,
            "$in_merge": false,
            "id": "XXXXXX",
            "Tag": [],
            "$approval_state": "approved",
            "$pathfinder": null,
            "$approved": true,
            "Unit_Price": null
        }
    ],
    "info": {
        "per_page": 200,
        "count": 1,
        "page": 1,
        "sort_by": "id",
        "sort_order": "desc",
        "more_records": false
    }
}

I believe it may be a bug?

Thanks,

Cindy