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.

It happens when IsRestrictedWhenMaximized set to true.

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.

Setting the Owner property to null in order to detach the minimize behavior of linked RadWindow instance to its owner does not take effect unless the RadWindow instance is closed and reopened.

Available with the R3 2016 SP1 release. 

Available in LIB version 2015.3.1130, it will be also available in the 2016 Q1 Release.

Available in the 2015 Q3 Release.

Property for example.

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.

The thrown error is that the element that should be set as FocusedElement cannot be found.

Available in LIB version 2016.2.606, it will be also available in the 2016 R2 SP1 release.

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

RadWindow.Confirm default button is OK, in order to change that presently we have to extract and modify styles, set FocusManager.FocusedElement binding to Cancel and set the ContentStyle property in code. 
It would be much more user friendly if this could be controlled by a simple property.

In WPF browser application it is possible to move the focus of a focused TextBox control inside the RadWindow to the parent page with Shift+Tab keyboard combination

When creating themed applications using RadControls, the standard Windows MessageBox control looks out of place.  With that in mind, the predefined RadWindows (Alert and Confirm) seem to be natural replacements for a typical MessageBox.  

However, when these dialogs open, they are silent  That is, they don't play any error, warning, or question sounds like the standard MessageBox - which makes them seem "strange" when used as a replacement.

Adding sounds to (for instance) the Alert window is fairly simple and can be accomplished like this:

RadWindow.Alert(new DialogParameters()
{
    Content = new System.Windows.Controls.TextBlock {
        Text = ex.Message, Width = 250, TextWrapping = TextWrapping.Wrap },
    Header = "Update Error",
    Opened = (alertDialog, eventArgs) => System.Media.SystemSounds.Exclamation.Play()
});

Though, it'd be nice if the ability to play a sound was built-in.  I'd suggest that the DialogParameters class used to customize the predefined dialogs be extended to support a SystemSound member of type System.Media.SystemSounds which, if defined, would play the specified sound when the dialog opens.

The default dialogs for the WPF RadWindow (Prompt, Alert, Confirm) do not seem to allow sizing of the content of the message. I have tried imbedding controls to set width and maxwidth, but I need to use a MaxWidth to prevent horizontal scrollbars. Ideally a Maxwidth parameter would be available allowing longer text message to spread out.

The code below works, but I'm restricted to a narrow dialog.

            Dim Scroller As New ScrollViewer
            Dim TextBlk As New Controls.TextBlock()
            With Scroller
                .HorizontalScrollBarVisibility = ScrollBarVisibility.Disabled
                .VerticalScrollBarVisibility = ScrollBarVisibility.Auto
                If Owner IsNot Nothing Then
                    .MaxHeight = (WPFScreen.GetScreenFromElement(Owner).WorkingArea.Height - 100) 'Do not use entire height
                Else
                    .MaxHeight = (WPFScreen.Primary.WorkingArea.Height - 300) 'Do not use entire height
                End If

                With TextBlk
                    .Margin = New Thickness(10)
                    .TextWrapping = TextWrapping.Wrap
                    .Text = Message
                    'We seem to be stuck with a fixed width available for our text.
                    'If this is increased a horizontal scrollbar appears.
                    .MaxWidth = 230
                End With
                .Content = TextBlk                  'Put textblock in scroller                 
            End With

            Dim RadDialog As New DialogParameters
            With RadDialog
                .Content = Scroller
                .DefaultPromptResultValue = DefaultValue        'Default prompt result
                .DialogStartupLocation = DialogStartupLocation
                .Header = Header
                .IconContent = IconContent
                If ThemeName.ToLower <> "expression_dark" Then ' *NoLoc*
                    .ModalBackground = m_SPIBackgroundBrush
                End If
                .Owner = Owner
                .Closed = New EventHandler(Of WindowClosedEventArgs)(AddressOf OnPromptClosed)  'Reference handler for response
                '.ContentStyle
                '.WindowStyle            
            End With

            RadWindow.Prompt(RadDialog)

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.

The property is present, but it is not implemented.