That's normal for a 1.6 gallon toilet flush. They still need some pressure, so they have to have some water in the tank to make what does go out leave with some force. The flapper valves are made to close earlier than the "old" ones did, keeping the total volume of water down to the spec. Now, if you have a really big load, you can hold the lever down until it all goes out, but then you'd be using more water with each flush. If it is designed right, it shouldn't make a difference! (it should flush right by design).