Let's be clear here...the Drake is designed to dump about 1.6g on a flush. To do this, you need to push the flush lever down fully, but not hold it. If you don't push it down fully, it won't stay up on its own to allow the normal flush volume. This is true with many toilets. A quick flick won't allow it to do its thing as designed. Holding it down until the tank empties defeats the purpose of the low-flow toilets, and for nearly 100% of the time, is a waste of water...the Drake, and most of the better toilets DO NOT NEED more than the design water volume. So, if you 'flick' some but hold it down to empty the tank on others, you'll likely end up using more water than if you did it as designed for each flush.
Let's stop calling this a 'feature', since it isn't and can lead to waste, which we are trying to avoid. It isn't unique to this line of toilets, either; my old 3.5g job (non-Toto) would do the same thing.