The reason is that alcohol has a specific gravity of .8 vs water is a 1. What this means is that it is thinner in nature than water. Becuase its thinner, things dont like floating in it. So what happens is it sloshes more, and the float has a harder time stying in an open position.
What does this mean... just like the gas guages that bounce when they start getting lower, the activity of the LED will let you know how much you have left by the way it flashes. The lower the level the more prone it is to blink under accelleration. What your really watching for is that the LED is not lit when the vehicle is standing still.
There is a new tank/float design i've been using now for the last 3 months.. it appears to be better as to the blinking.