By default the Design view of the RadMarkupEditor has no horizontal and vertical scrollbar. By using the following code, I was be able to show the scrollbars:
oDesignView = mEditor.GetType().GetField("designView", BindingFlags.NonPublic | BindingFlags.Instance).GetValue(mEditor) as WebBrowser;
oDesignView.ScrollBarsEnabled = true;
However, it has a side effect which I find rather annoying. See the screenshot in attachment to see the effect. The vertical scrollbar appears next to the "default" scrollbar. For the horizontal scrollbar there is no such problem. Is this a known issue and is there a way to avoid this behavior?