When implementing custom binding with the Telerik ASP.NET MVC, I based my code on this example described here under the Controller tab.
The CustomBinding action is called when the whole page is loaded or refreshed, then showing on the grid the default data, e.g. the first page. This action should return a view with the model object (IEnumerable<Order> in this example).
Although the Telerik example is right, when I wrote my code based on it, I mistakenly used the wrong model object, and couldn't figure out what was wrong. Thanks for this forum post that enlighted me of what was going on.