if promise fails to create busy never completes

[SteveDrakey]

Using angular2-busy I lock the UI when a http request is running.

this.loginFail = !await (this.busy = this.authenticationService.login(this.username, this.password));

I only have one promise, if the promise fails to create ngBusy just keeps spinning, to make it fail I try to request from error:/ as follows :

async login(username: string, password: string): Promise < boolean > {
    try {
        var r = await this.reCaptchaHttp.post('error:/', {
            Email: username,
            password: password
        }).toPromise();
        var JWTToken = r.json();
        return true;
    } catch (e) {
        // snip. we have more code but its not relevent
        return false;
    }
}

But, if I add

await this.delay(0); 

It works fine.

And the delay code

async delay(ms: number) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

If I remove await this.delay(0); it never stops spinning.

If I debug the code, when it works busy looks like (note, I still have an exception in the case but its thrown by the server so the http request has completed although in error)

ZoneAwarePromise {__zone_symbol__state: true, __zone_symbol__value: false, busyFulfilled: true}

When it fails ( error before http request )

ZoneAwarePromise {__zone_symbol__state: true, __zone_symbol__value: false}

And with my delay

ZoneAwarePromise {__zone_symbol__state: true, __zone_symbol__value: false, busyFulfilled: true}