[BUG] CenterStack/VerticalStack/... memory issue #193
Description
When a window contentView registered with some popup(s) is terminated, it's associated stack is not killed in memory. And when a window with the same type is created, a stack will again be created in memory.
This means when I continually launch a window with registered popups and terminated it, the number of stacks in memory will only increase and never decrease.
