When the Window is opening or resizing and Winforms controls are placed inside its content the content flickers.

Make it possible to be able to drag the Window not only from its Header. In some cases it is useful to be able to drag the RadWindow from within its content.

When a modal RadWindow is opened clicking out side of the Window (the overlay) should make a the Window blink and a sound should be played.

Currently the template of the dialogs should be customized:
http://www.telerik.com/community/code-library/wpf/window/how-to-modify-the-alert-dialog-icon.aspx

Available in the 2016 Q1 Release: Added an IconTemplate property that provides an easier way to change the predefined dialogs' exclamation/question mark images.

If a ContentControl is placed inside the control and the ResizeMode is set to NoResize the SizeToContent doesn't take effect.

As a workaround all you need to do is set the ResizeMode to NoResize in the Loaded event of the ContentControl.

Make it possible to add "No" button to the predefined RadWindow.Confirm dialog without the need of custom Template.

rendering problem is when minimized only

It can be reproduced with the Show method of the window or with Dock, ToolWindows and the save - load functionality.

When the attached TextOptions.TextFormattingMode="Display" property is set to the RadWindow the window stops auto resizing its size according to the size of its content.

It would help to use RadWindow like System.Window with:
- WindowInteropHelper for correct modal behavior
- Set window in task bar, also set taskbar icon/title
- Use RadWindow as MainWindow in Application (set Application.MainWindow property with RadWindow 

PreviewClosed event is called twice when using custom close button in DialogWindow

This is WPF only and not applicable for Silverlight.

Popup shows behind RadWindow when using two monitors in Windows XP.

As a workaround you can set:  window.CaptionHeight= 0;

Available with the R3 2016 SP1 release.