If you drag the pane from one RadDocking element to another, the ActivePane of the docking that started the drag operation is not cleared. The ActivePane should be updated (set to null, or updated in accordance to the PaneActivationMode setting) because the corresponding pane is no longer in this RadDocking instance.

To work this around, you can subscribe to and manually update the ActivePane property.

   private void RadDocking_LayoutChangeEnded(object? sender, EventArgs e)
    {
        var docking = (RadDocking)sender;
        if (docking.ActivePane != null && !docking.Panes.OfType<RadPane>().Contains(docking.ActivePane))
        {
            docking.ActivePane = null;
        }
    }