Sum of currentActive and currentInactive not equal to currentOpen transactions

function repro() {

    nthreads = 10

    db.createCollection("c", {writeConcern: {w: "majority"}})

    threads = []

    for (var t=0; t<nthreads; t++) {

        thread = new ScopedThread((t) =>  {

            var ses = db.getMongo().startSession()

            ses.getDatabase("test").c.insert({_id: t, i: 0})

            for (;;) {

                try {

                    ses.startTransaction()

                    ses.getDatabase("test").c.update({_id: t}, {$inc: {i: 1}})

                    //if (t==0) sleep(1000)

                    ses.commitTransaction()

                } catch (e) {

                    print(e)

                }

            }

        }, t)

        threads.push(thread)

        thread.start()

    }

    for (var t = 0; t < nthreads; t++)

        threads[t].join()

}