Hello, Trustteam,

Note, when you inherit from a RadControl (or any RadControl descendant), the original control themes are not automatically inherited. In order to guarantee that the custom control that you use will get the desired theme you should override the ThemeClassName property of the descendant of RadGridView as shown below:

public partial class TkGrid : Telerik.WinControls.UI.RadGridView
{
    public override string ThemeClassName
    {
        get
        {
            return typeof(RadGridView).FullName;
        }
    }
}

You can see the result in the gif file. I modified the provided project accordingly. More information is available here: https://docs.telerik.com/devtools/winforms/telerik-presentation-framework/inherit-themes-from-radcontrols-derivatives 

I will change the status of this bug report to Declined since this is not an issue.

Should you have other questions do not hesitate to contact me. 

Regards,
Nadya
Progress Telerik