I don't think ViewStack is meant to be used like that. The only time ViewStack can have a selectedIndex=-1 is when there are no children in it.
If you want to show an empty container, maybe you can create an empty box or canvas with no background and adding that to the ViewStack as a child. Or set the ViewStack visible property to false.
ok but I need a way of having it so that the linkbar for the viewstack does not have a default selected index. is that possible?
Hmm, that's an interesting use case. Have you tried using ToggleButtonBar instead? You can achieve what you are trying to do by setting selectedIndex to -1. If you must use LinkBar, I would suggest not tying the LinkBar to the ViewStack and managing the interaction between the two in custom code.