rendering problem is when minimized only

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.

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.

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.

Available with the R3 2016 SP1 release. 

Available in the 2015 Q3 Release.

The Window doesn't resize correctly when dragged from the primary monitor (with taskbar) and docked to the top of the screen of a secondary monitor (no taskbar) in order to maximize it and "Show window contents while dragging" Windows system setting is disabled.

This happens when RadWindowInteropHelper.AllowTransparency is set to False and RadWindow is implemented as UserControl. The Window need to be maximized firstly on the main screen and then on the secondary in order for issue to be reproduced.

The issue also affects the ToolWindow that RadDocking uses for its floating Pane. In order to reproduce the problem, the primary monitor needs to have its DPI higher than the secondary one.

The header buttons elements are not on the proper places when the window is on a monitor with different DPI. To reproduce this the DPI of the monitors should be different for example 125% (main) and 150% (secondary). Also, to reproduce this you will need to enable the DPI awareness of the application by setting the dpiAware and dpiAwareness settings in the app.manifest file.

Moving a window fast on low performance machine or between two monitors causes incorrect offset to be applied to the mouse cursor

Maximizing RadWindow from the header button shows a window with the size of the content if SizeToContent = true. If you maximize with double click on header it is ok.

This is reproducible when you disable the automation peers by setting the AutomationManager.AutomationMode static property to Disabled.

It happens when you open a new RadWindow dialog (using the ShowDialog method), and the close it. After this, when you interact with the main window (click a button, hover a GridView, etc.) the exception occurs.

The exception is thrown only in the Output pane of Visual Studio and it doesn't cause any harm to the application. You can safely ignore it.

The exception message is "Invalid window handle".

To work this around you can enable the "Enable Just My Code" option in Visual Studio.

When the RadWindow is initialized on a monitor and then another monitor with higher resolution is added during runtime, moving the RadWindow to the monitor with higher resolution, causes the RadWindows' width and height to be limited to the ones of the initial monitor.

After fixing this BUG (Release LIB 2019.3.930), an additional issue is found.

A window is in Maximized or Normal state, click on the application icon in the taskbar to minimize it and click again to restore the window. It gets clipped to ~160*26 pixels. After clicking on this header, it gets restored to Maximized or Normal state depending on the initial state.

I have a two-monitor setup with identical resolutions (FullHD on both monitors) and Scale is 100% on both monitors.

This exception is thrown when the CanExecute method of the Command bound to a response button returns false when the response button key is pressed. 

If RadWindow has its Width set to a value greater that 50% of the screen and that window is snapped to the left or right, performing minimize and then restore leads to incorrect normal size .

Available in LIB version 2015.3.1123, it will be also available in the 2016 Q1 release.