Any time I want the same control to show up in multiple tabs, I prefer to place that control on top of the tab control, rather than inside it. At edit time you might see a "shadow" indicating that the item is on top of the tab control, but that will go away at run-time (or switch to Run mode to see the difference, by hitting control-M). Then you can use the control's visible property to hide it for the tabs where you don't want that item visible.
I haven't checked that this works specifically with subpanels but it definitely works with other controls, and it appears that subpanels do support the Visible property.
