Themed Usercontrol

[google]

I'm trying to add themes to a usercontrol. I've added the Themeable
attribute to it and its fine at run-time. At design time a page with
the control in returns "There was an error parsing the theme: Type
'System.Web.UI.UserControl' does not have a public property named
'HeaderStyle'"

(Theres very little code and alot of controls so I'd rather not use a
custom control)

Any help would be appricated,
Graham