Keep in mind that shorts can't short what they've...

Keep in mind that shorts can't short what they've already shorted, when they're already short shares the only move they can make next is to buy them back. There's not an unlimited number of shares to borrow as ASIC is very good at regulating the practice of naked shorting, and the way in which total shorts as a percentage of shares outstanding has seemed to plateau over the past few months indicates to me they may be struggling to find more shares to borrow at a reasonable rate.

Given the size of shorts leading up to this announcement, it'll be rather difficult for them to "push" the price down if it's a great announcement, especially if the company quickly follows it with an aggressive buy back. They'll need to be more focused on closing their positions (so buying, not selling)