When the TitleBarVisibility is Collapsed, the backstage close button is aligned with the top of the backstage adorner. The button should have a top margin applied. 
This reproduces when the BackstagePosition property of RadRibbonBackstage is set to Office2013, which is the default setting of newer Telerik themes.

To work this around, get the backstage close button and set its top margin.

 private void RadRibbonBackstage_Loaded(object sender, RoutedEventArgs e)
 {
     var backstage = (RadRibbonBackstage)sender;
     var closeButton = backstage.FindChildByType<RadRibbonButton>();
     closeButton.Margin = new Thickness(closeButton.Margin.Left, 15, closeButton.Margin.Right, closeButton.Margin.Bottom);
 }

NullReferenceException is thrown when the RadVirtualKeyboard control gets loaded, but it is not added to the visual tree. This skips the initialization of an internal collection which is used on Loaded, thus throwing the error.

To work this around, you can manually call the OnApplyTemplate method of RadVirtualKeyboard before it gets loaded.

virtualKeyboard.OnApplyTemplate();

When RadRichTextBox for WPF is hosted in a WinForms application (through ElementHost), typing with Japanese IME duplicates the typed letters, which makes the control unusable with the default behavior.

Possible workaround: Create custom caret. There are some suggestions in this forum thread: https://www.telerik.com/forums/richtextbox-doesn't-support-japanese-ime-when-hosted-in-winforms