This applies to data bound containers like grid template columns. 
For standalone control instances, see how to use the DataSelectedField here: https://docs.telerik.com/devtools/aspnet-ajax/controls/radiobuttonlist/data-binding/server-side-data-binding

When the items in the RadRadioButtonList are declared in the markup, the SelectedValue='<%#Bind("fieldName") %>' approach works as expected, but when the items are fetched from a data source, no item is pre-selected.

This works with the standard asp:RadioButtonList and so it must work with RadRadioButtonList.

Issue explanations and workarounds are available in the attached sample pages and videos below.

In short, the workarounds are:
- use declarative items when possible
- OR, use an <asp:RadioButtonList> and a <telerik:RadFormDecorator> to get uniform appearance of the radio buttons across browsers