They have really screwed with the way Base Pages and Base Controls work (and not necessarily for the better). The new migration wizard will detect your base pages and controls and attempt to move them to the new ASP.NET 2.0 way of doing things. The @Page and @Control compiler directives now support an attribute called CodeFileBaseClass. During mirgation, the wizard automatically converts any page or control that does not inherit from Page, Control, WebControl, UserControl, HtmlControl, or HtmlGenericControl. It's definitely a different way of doing things and I am not sure if I necessarily like it.
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