A memory leak related to the automation peers of the RadPane and RadPaneGroup appears when you close a pane (using its Close button) even if you call its RemoveFromParent() method.
To work this around disable the automation peers. To do so please set the static AutomationManager.AutomationMode property toAutomationMode.Disabled.
AutomationManager.AutomationMode = AutomationMode.Disabled;
The issue originates from ItemsControlAutomationPeer. It is reported to Microsoft in their old connect portal here =>