When you make a change that results in a resize of your child control(s), the layout engine will automatically lay them out as you correctly say. You need to manually call the FitContents method of your parent pane after this to have it resize itself around the new controls.
We have added another property for the next build called AutoFitContents, which will automatically keep the pane just the right size to accommodate its child controls. This is used together with AutoLayoutChildren.