The error could only be replicated if you did not set the DataKeyField in the WebGrid table correctly. In my test you will need to set the DataKeyField during page load and after RetrieveStructure during PrepareDataBinding. Here is the snippet for PrepareDataBinding event handler:

void _grid_PrepareDataBinding(object sender, DataSourceEventArgs e)
{
    if (!Page.IsPostBack)
    {
        _grid.RetrieveStructure();
    }

    _grid.RootTable.DataKeyField = "CustomerID";
}

My test also indicate that the PerformBatchUpdate function still fails to update the Grid during postback. The bug report has been reactivated and being investigated by our developer.

In  my environment, I could not replicate the error you encounter. My environment is using the latest build of  WebAqua 2 and WebUI Silverlight Framework 1, build 221 and build 104 respectively.

Did the issue also occurs in our provided FishEye Silverlight sample?

Do you mind sending us a sample project in order for us to replicate the issue in our environment? 

As far as I know, WebGrid will only accept boolean value for checkbox column.

For your scenario, you will need to add a new boolean column during InitializeDataSource server side event and during InitializeRow server side event you will need to set the boolean column based on the Y on N value.

Attached is a simple sample of such scenario 

Attached is a simple sample page that I create in order to recreate the issue you are facing.

In my test, after postback the WebGrid will keep it state after postback (sort and filter). The test is using the latest build of WebGrid 7 and WebUI Framework 3, build 403 and build 752 respectively.

Regarding the PagingExportMode issue in self reference grid, the issue is currently still open.

Our developer is currently focusing on the WebUI Studio 2010 R1 release, so the self reference grid export issue fix is currently being planned for May release.