This behavior was originally reported over 12 years ago and has not received significant demand or follow-up from the community since then. Considering this and the availability of a workaround, we are unable to prioritize it over more impactful and widely requested improvements.

If this limitation is still affecting your scenario, please share additional context or use cases. This will help us better assess the severity and reconsider prioritization in the future. Thank you!

Regards,
Martin Ivanov
Progress Telerik

Until this issue is resolved you could workaround this issue like follows:
- use the loaded event of the window to get the TemplatePart holding the Image -> "PART_Icon"
- set its width and height to the default size 16x16.

void MainWindow_Loaded(object sender, RoutedEventArgs e)
        {
            var image = this.ChildrenOfType<Image>().FirstOrDefault(x => x.Name == "PART_Icon");

            if (image != null)
            {
                image.Width = 16;
                image.Height = 16;
            }
        }