React MobX error with 08_create1k-after10k

[krausest]

Currently the benchmark 08_create1k-after10k fails and quite a strange way after updating react and mobX (5.0.3, no matter if react 16.1 or react 16.4). It worked fine with mobX 3.3.1.
Creating 10,000 rows and then appending 1,000 causes a loss of the first 10,000 rows. If I change the number of rows created at first to 1,000 it works as expected - sounds strange.

Click create 10,000 rows:

As expected there are 10,000 rows. Then click on append rows:

Here the strange thing happens. This is the modified add action:

    @action add() {
        console.log("store.add length before", this.data.length);
        this.data = this.data.concat(this.buildData(1000));
        console.log("store.add length after", this.data.length);
    }

It shows that there are 10,000 rows in the store after the add call. But as one can see the row ids have changed and only 1,000 rows are left.
Fun fact: It works correctly for any row count < 10.000
@mweststrate Can you please take a look?