Currently, a stack is dependent on the stacking order of the layers.

Usually, that doesn't cause any trouble. But I have grid layout (aka table) where a context menu needs to fly up instead of down. To prevent the menu from ending up under the rows above, I have to break the stack so I can reverse the layer order (ie the row at the lowest y value needs to be at the highest z value).

Ideally, a stack would not depend on layer order.
Alternatively, you could just allow for reversing the logic somewhere, like a sort flip control.