I have answered your ticket and I am pasting my response here for anyone else that may have a similar question and stumble on this thread:
RadHtmlChart works entirely on the client, so it also binds on the client to its data, so the server items collection is empty, and this is the expected behavior of the control: http://docs.telerik.com/devtools/aspnet-ajax/controls/htmlchart/troubleshooting/known-issues/known-limitations.
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