In my experience with Airbus, below a certain RA the autothrottle will not respond to a speed loss below Vref. This can lead to quite a surprise with a gusty tailwind in flare. As the thrust levers are still in the detent there is nothing you can do to spool the engines up except go-around. Difficult to recognise and deal with in a short space of time: note this is not a criticism of the aircrew in this situation.