Example code of the problem can be found here
The resize event is handled inside the controls that are client of the radpane.
The RadPane.SizeChangedEvent event isn't firing indeed. I think this event should fire if the RadPane changes size, the name suggests exactly that. What other event is sent when the RadPane does change size?
I wanted to make a grid in the pane where the header has 10% of the pane with a given minimum and maximum height. Using a grid you just can declare this in the style. However because the RadPane.SizeChanged event wasn't firing when resizing the header height wasn't updated. I changed all client controls to set the header size of the parent when the control is resizing, not a nice solution but it worked. But now the client control does not get resize events anymore.