The backdrop closed the picker on mouse_down but didn't consume the
event. The same press would propagate to the top div and the same
click sequence's mouse_up could then land on whatever element ended
up under the cursor (a tab, a button) once the backdrop unmounted on
the next render — dismissing the popover would inadvertently fire a
second action.
Add `cx.stop_propagation()` after the close so the dismiss click ends
at the backdrop. Standard popover semantics: outside-click closes,
consumed.
ZacharyZhang-NY
cd4bac8e22