Tis has something todo with the formula, on some points there are values multiplied by your rate. So, since your rate was still 0, it got multiplied by 0 which makes 0 again.
This means too: if you would have got 0.5 rate it would have been divided. But as soon as you reach 1 rate, your rate gets multiplied by 1 or higher (depends on your rate again).
Hope this explains why,
Paul