The investor has a choice when it comes to the amount of the roll over of the deposit.
They can choose to take out the interest earned on the existing deposits and just continue with the initial deposit amount.
This is more likely when the interest is being paid out.
In case of a cumulative deposit the investor can reinvest the whole amount with the interest accumulated or they can take out the interest and reinvest just the initial amount.
Giving the right instructions to the bank is essential in making the choice for the investor,