The financial crisis has provided a vivid example of how financial instability can force the hand of monetary policy. When the burst of an asset bubble threatens a collapse of the financial system, the meltdown will in all likelihood have severe consequences for the real economy, with corresponding downside risks to price stability.
In that case, monetary policy is forced to mop up the damage after a bubble has burst. And, confronted with a financial system that is still in a fragile state, monetary policy might be reluctant to embrace policies that could aggravate financial instability.