RadioButtonList Items collection not persisting

I have a custom WebControl which renders a RadioButtonList.  When the WebControl first gets loaded I bind the RadioButtonList's datasource.  This will popuplate the Items collection within the RadioButtonList.  But when the postback occurs the Items collection for the RadioButtonList is empty.

If I create a custom RadioButtonList on its own the Items collection will persist.  But If I try to throw this RadioButtonList into a WebControl, the Items collection does not persist....why is this so???
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