StackView: transitions are broken

1) run examples/quick/controls/theme
2) press 'push'

expected behavior:

• current page transitions out & new page transitions in

actual behavior:

• new page transitions in, but the current page doesn't transition out

3) press back

expected behavior:

• current page transitions out & previous page transitions in

actual behavior:

• current page transitions out, but the previous page is immediately in place without appropriate transition