Maybe you just have too much water in the tank? I just unplugged my tank, and when i do that, the water level drops down maybe 1/4-1/2" from the bottom of the "Deskmate" text, and then when it gets plugged back in it goes right up to the bottom of that text.
These two pictures are my water level when the tank is UNPLUGGED.
These two pictures are my water level when the tank is UNPLUGGED.