Arduino won't go to sleep!

Projects Programming
2

I think this really simple program should blink a few times and go to sleep forever.
But it blinks 4 times, goes to sleep for about 60 seconds, and then starts blinking forever.
Arduino 1.0 Arduino Pro Mini 328 3.3V powered by FTDI basic 3.3V serial converter from USB

#include <avr/sleep.h>
#include <avr/power.h>

int I;

void enterSleep(void)
{
  set_sleep_mode(SLEEP_MODE_IDLE);
  
  sleep_enable();
  
  /* Now enter sleep mode. */
  sleep_mode();
  
  /* The program will continue from here after the timer timeout*/
  sleep_disable(); /* First thing to do is disable sleep. */
  
  /* Re-enable the peripherals. */
  power_all_enable();
}

void setup() {                
  pinMode(13, OUTPUT);  
  I = 5;  
}

void loop() {
  while (I-->1){
    digitalWrite(13, HIGH);   // set the LED on
    delay(1000);              // wait for a second
    digitalWrite(13, LOW);    // set the LED off
    delay(1000);    // wait for a second
  }
  enterSleep();
}