Since drag-to-day (#891) a place pin swallows mousedown so the map holds
still while a drag starts. Leaflet only clears its "the map was panned"
flag on a mousedown it sees, so after one drag of the map it took every
later click on a pin for the end of that pan and dropped it. Pins stayed
dead until something else on the map was pressed, which is why zooming
out and clicking a cluster brought them back. Trip planner and
collections map were both affected; the GL renderers never were.
Pressing a draggable pin now clears that flag itself by switching the
map's pan handler off and on again, which is what the map would have
done had it seen the press. The click keeps Leaflet's normal route, so
it still closes an open popup on the map and still reaches listeners on
the page, such as an open context menu.
The new test file drives a real Leaflet map, since the mocked
react-leaflet has no pan state to go stale.
Maurice