Bug in buffer or bufferCount operation when used with subject

[iFadey]

RxJS version: 5.0.0-beta.8

Code to reproduce:
https://jsfiddle.net/iFadey/qahvL1dm/

let section = document.querySelector('section');
let subject = new Rx.Subject();

Rx.Observable.fromEvent(section, 'click')
.subscribe(e => subject.next(e))
;

subject.buffer(subject.bufferCount(2))
.subscribe(x => console.log(x))
;

Expected behavior:
On first two clicks on section element must print pair of two event objects.

Actual behavior:
It prints single event object on first two clicks. Afterwards it starts printing correct pair.

Additional information:
I verified it in RxJS 4 and it works correctly with that version.

[benlesh]

To narrow this down, what you're seeing is happening in buffer. The same behavior occurs with subject.buffer(subject.take(2)). This seems a little edge-casey, and might be a quirk with changes to default scheduling, but, for now I'll label it as a bug until we can confirm otherwise, since it is odd.

[mpodlasin]

Currently on

const source = Observable.from([1,2,3,4,5,6]);
source.buffer(source.take(2));

RxJS 4 returns:

[1]
[2]
[]
// complete

This last array is last opened buffer, which did not have time to be populated with values, since right after it's opening take(2) completes stream.

The same code in RxJS 5 results in:

[]
[]
// complete

There are actually two differences here: first is obvious subscription order bug, that was fixed here: #2195

On that branch results are:

[1]
[2]
// complete

So second problem is that last one array. Currently code

Observable.never().buffer(Observable.empty());

in RxJS 4 results in

[]
// complete

and in RxJS 5

// complete

So real question here is: when selector stream completes do we want to return last initiated buffer?

There is also similar bug fix #2174, but in other direction - it emits last buffer once source observable completes