Issues with dynamic property

1. Dynamic property doesn't support non-primitive data types
   We are trying to build an odata data service to enable clients to store arbitrary json data. I define an open data type by adding the following field. It works well with primitive data types like string ect.

public IDictionary<string, object> DynamicProperties { get; set; }

However, when I try to post an item with the following dynamic property.

"SortKey": {
    "Timestamp": "0001-01-01T00:00:00+00:00",
    "KeyValue": 0
}

I got an exception below.

The given untyped value '{"Timestamp":"0001-01-01T00:00:00+00:00","KeyValue":0}' in payload is invalid. Consider using a OData type annotation explicitly.

Is there a way to support arbitrary json data and return them as-is on request?

2. Filtering dynamic property always return empty result
   I posted some items with a dynamic property "type": 65. However, I always get empty result with $filter=cast(Type, 'Edm.Int32') eq 65.

I stepped into the source code. It seems like this check statement is causing the problem. It works well if I skip it under debugger.
https://github.com/OData/WebApi/blob/13938e80d0754f2e554f70c8e92fba1baeaf8318/src/Microsoft.AspNet.OData.Shared/Query/Expressions/ExpressionBinderBase.cs#L1370

Is this an known issue? Any comments are highly appreciated. Thanks!