tracking `unload` events with `buffer`

[jney]

I'm tracking events on a web page events$.buffer(/* ... */).subscribe(/* ... */).
One of my source event is the event unload which generate a buffer. But i never can get the generated buffer.

const opening$ = Observable.return({})
  .concat(unload$)
  .flatMapLatest(x => Observable.timer(0, 2000))
  .skip(1)

events$.buffer(opening$).subscribe(buffer => {
  // i never go there on 'unload'
})

Any idea why ? Or how can i fix this ?