Rejected with the following comment:

When trying to enable/disable an input element that is decorated with RadFormDecorator, the disabled attribute must be set to the DOM input element and not to the JavaScript input object, in order for the RadFormDecorator to take effect. For example:
ASPX:
<telerik:RadFormDecorator ID="RadFormDecorator1" runat="server" DecoratedControls="All" />
<telerik:RadButton ID="RadButton1" runat="server" AutoPostBack="false" OnClientClicked="disableCheckBox" Text="click" />
<input type="checkbox" id="checkbox" name="name" value="sdf" checked="checked" />
JavaScript:
function disableCheckBox() {
    var checkbox1 = $telerik.$('#checkbox');
    //Either
    //checkbox1.prop('disabled', 'disabled');
    //OR
    checkbox1[0].disabled = true;
}
In IE there is an issue with the disabled property of the DOM elements, when it comes to tracking it. This issue is reproduced only when the element is enabled and should become disabled. The other way around the tracking is working, i.e. if the select is disabled it can be enabled and IE will raise an event about it. This is a browser issue and there is nothing that can be done on our side to work around it.