Thank you for the accurate information.
Sure the uImage I used for testing is attached. I echo "mem >/sys/power/state" and press the push button to alter it's state, repeatedly for dozens of times things are working fine. You may also attach your uImage so I can try it on my board.
We actually also found this maybe related with the hardware, on some boards it does not work so smoothly, we are in further investigation over this, it would be very helpful if you could provide us with 1) silicon version of your BF609 chip, it's on the top of the chip, a string like 0.0, 0.1 or 0.2. 2) version of your ezkit board, it's a string on the board.