It happens in yocto 2.0 and 2.1 that if you press the power button for 1-2 seconds and leave it the LED flashes continuously. Even if you reboot the board it will again start to flash continuously. The only fix I found to this was by reflashing the firmware. Obviously that is not the right solution but I dont know.
I just read that the power switch when pressed shortly for 1-2 seconds take the edison into low power sleep mode. May be that is what is making it flash but I do not know how to come off of it.
Pressing the power button for 2 to 7 seconds will turn the AP mode on and the LED will start blinking. To turn off the AP mode you should press the power button again for 2 to 7 seconds. If you press it for more time the Edison will enter into the low power sleep mode.