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.

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

If the autohiding feature of the taskbar is enabled and RadWindow is maximized, the taskbar is not displayed when the mouse is over the bottom of the screen.

This is observed also in RadTabbedWindow.

1) Open WPF Demos and maximize it
2) Open "Alert, Prompt and Confirm" sample
3) Click "Confirm"
4) Minimize all windows (for example, by using Win+D)
5) Switch to WPF Demos again
6) Now you can't do anithing with the window, even close it. You can use task manager to close it.

If you have set SizeToContent of RadWindow to true and you use one of the following options, SizeToContent will not work.

- UseLayoutRounding = true
- TextOptions.SetTextFormattingMode(dialog, TextFormattingMode.Display);

Available in the 2015 Q3 Release.

Place Expander as content in RadWindow. Once expanded, the SizeToContent feature stops working as expected.
Available in the 2015 Q3 Release.

If you open the window on a specific resolution, maximize it and then change the resolution to a bigger one, the window size is not updated. The window stays in the original resolution of the screen.

To work this around subscribe to the SystemEvents.DisplaySettingsChanged event and reset the WindowState of RadWindow.

public MainWindow() // where MainWindow is RadWindow
{
	InitializeComponent();
	SystemEvents.DisplaySettingsChanged += SystemEvents_DisplaySettingsChanged;
}

private void SystemEvents_DisplaySettingsChanged(object sender, EventArgs e)
{
	if (this.WindowState == WindowState.Maximized)
	{
		this.WindowState = WindowState.Normal;
		this.WindowState = WindowState.Maximized;
	}
}

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.