RadControls for ASP.NET Ajax as their name suggest are controls designed for ASP.NET Web Forms. They are not intended to be used in MVC scenario since they are using ViewState and server-side binding and events which are not available with ASP.NET MVC.
There are certain scenarios where one could make the control to be displayed on the page but not to behave as intended. The case with RadPivotGrid is that this control does not support any of its features inside MVC.
I hope the provided information helps.
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