Can you share more information about the given scenario? If you could send us a ticket with attached sample project it will shed some light on the problem.
Please, note that placing a RadPaneGroup within a RadPane is not a supported scenario - it must be placed into a RadSplitContainer. Here you can find useful information about the RadDocking layout - http://www.telerik.com/help/wpf/raddocking-getting-started2.html
the Telerik team