JSONStore cannot load data when level goes beyond 3 layers deep

[webarnie]

I defined a JSONStore and mapped my JSON data. Once I go beyond 3 layers deep, the store fails to load and no message is written to the console. The store was originally coed with designer and by right clicking I was able to load the store. Recently the JSON structure changed, so I changed the mapping and the store fail to load. I went back to designer and implemented the changes and could not load the store there either. I defined a second JSONStore and move field to that store loading it after each field move. Once I hit a field that mapped 4 levels deep, the store stopped load.
Since EXTJS is supposed to support JSON data I find this surprising. Is there a limitation that is not well documented? Is this a bug? If there is no limitation and this is not a bug, how do you map the following

JSON data

{
    "success": true,
    "message": "",
    "total": 1,
    "data": [
        {
            "InquiryAccountSummaryResponse": {
                "AccountSummary": {
                    "accountNumber": "N000210900",
                    "BillDetails": {
                        "processDate": "2011-05-18-04:00",
                        "dueDate": "2011-05-18-04:00",
                        "minimumDue": 21.12
                    },
                    "NextBillDetails": {
                        "processDate": "2011-05-18-04:00",
                        "dueDate": "2011-05-18-04:00",
                        "minimumDue": 12.21
                    },
                    "PolicySummaries": [
                        {
                            "PolicySummary": {
                                "PolicyDetails": {
                                    "policyNumber": "4003003599"
                                },
                                "BillingDetails": {
                                    "paidAmount": 0.99,
                                    "unpaidAmount": 1.99,
                                    "pastDueAmount": 2.99,
                                    "BillingMethod": {
                                        "current": "Automatic Payment Plan - Bank Account",
                                        "previous": ""
                                    },
                                    "Installment": {
                                        "amount": 1234.99
                                    }
                                }
                            }
                        }
                    ]
                }
            }
        }
    ]
}