These buy-ins are due to naked shorting, where the seller did not confirm that shares were available for borrowing before he shold them short. The 3 day settlement period passes, and he hasn't found the shares to settle his short trade. The shorter was probably hoping that the stock would drop within those 3 days, but it didn't.

So the TSX does a forced buy-in at a 10% premium price and sends the (short) seller the bill.

Forced buy-ins are the clearest signal that naked shorting is occurring.