CBA is the biggest mortgage lender in the country.
Clearly, CBA is either trying to start to cut back lending (to reduce further exposure to the housing market - think the horse has bolted long ago) and/or that it is trying to protect it's balance sheet by demanding topping up (which is a recognition of a sharp deterioration in valuations).
This is a worring development for the CBA appreared to be the strongest of the big 4. That means other lenders are already having to do the same time (after all they have the same business model, same market, same customers, same risks).
I would think going forward, investors will multiple properties will be the targets of such moves for unlike the familiy home (supposedly one would try holding on until the last drop of blood as it were), the banks have the most to lose when these highly leveraged types get into trouble.
The cascading effect will be frightening as one investor alone can result in many properties having to be dumped onto the market at the same time.
Unfortunately, negative gearing has resulted in a nation of landlords (with little net worth, plenty of debt) with multiple mortgages that are now a ticking time bomb.
Seriously, in this scenario losing the deposit by walking away may be the best option yet.