RadHTMLPlaceHolder is just a browser html rendered over the Silverlight plugin. The HTML will disappear once the window is closed but will not be affected by animations and render transformations. So the few milliseconds RadWindow plays its closing animation you will still see the placeholder. On option would be to manually remove the HTML placeholder when the window starts to close. Other would be to remove the closing animation of RadWindow and third would be to use the new RadRitchTextBox with its basic HTML rendering. Note the RadRitchTextBox is highly agile and provide presentation for MSWord like text rendering with tables and images embedded however it is not a html browser and rendering HTML is limited to the basic bold, italics, tables, list elements etc. CSS and other advanced features may produce glitches.
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items