To reproduce:
- Add drop down items and set their color instead of setting the text of the items.
- Change the selected index and leave the control. 
- The first item is selected.

Workaround:
Class MyDDL
    Inherits RadDropDownList
    Protected Overrides Function CreateDropDownListElement() As RadDropDownListElement
        Return New MyDDLElemnt()
    End Function

End Class
Class MyDDLElemnt
    Inherits RadDropDownListElement
    Protected Overrides Sub EnterPressedOrLeaveControl()
        ' MyBase.EnterPressedOrLeaveControl()
    End Sub
    Protected Overrides ReadOnly Property ThemeEffectiveType As Type
        Get
            Return GetType(RadDropDownListElement)
        End Get
    End Property
End Class