Borrow to buy shares and keep dividend

BHP is able to borrow large sums at very low (sub 4%) interest rates for long terms. Since the dividend is about 8%, would it make sense for BHP to borrow then use the proceeds to buy-back shares? If the borrowing cost is at 4%, the cancelled shares save 8% in dividend payments, so the net effect is a profit of 4% per share bought back.

The share buy back will help stabilise the share price. The buy back of shares will reduce the amount of dividends to be paid out, even if the rate is the same, because those shares will be cancelled.

Of course, the amounts to be borrowed and shares to bought back don't have to be very much. Just the act of doing it will probably have a marked effect. So the net addition to debt would probably be very small.

Is there something I am missing with this idea?