Due not blinking once in a second (BlinkWithoutDelay or Blink example)

I just tested Arduino 1.5.2 BlinkWithoutDelay and Blink examples with Due and the led 13 (onboard “L” led) is not blinking once in a second. It looks like that the led state is changing in every four seconds. Why is it working like this? Upload is ok, no errors. I have not had this kind of problems when using Uno board.