Docking pane problem in tabbed mdi app

I have a problem with my tabbed mdi application: If I try to create a docking pane at the end of the MDIForm_Load sub, the pane is displayed but "outside" the commandbars - that means I tried to dock the pane at the left side of the window, the pane "moves" the beginning of the commandbars to the right ! Here is the code I use with v9.50:

Dim paneToolbox as Pane
DockingPaneManager.SetCommandBars Me.CommandBars
Set paneToolbox = DockingPaneManager.CreatePane( 1, 200, 120, DockLeftOf, Nothing )

I went through the the samples but I did not find a resolution...