Simple but wrong code

Please consider this code:

#define KEY_PORT PORTD
#define KEY_DDR DDRD
#define KEY_FUNC_SEL PIND4 // --> first key (Port D pin 4)
....
#define LED_PORT PORTB // Test led, to see action on keypress
....

#define FUNC_SEL_KEY 0x10 // First function --> first key (Port D pin 4)
....

int main() {
   init();

   while (1) {
     // waits indefinitely for keypress
   }
   return (EXIT_SUCCESS); // Never reached
}

void init() {
   cli();
   LED_DDR |= (1 << DDB0); // Led out Port B pin 0

   KEY_PORT |= (1 << PORTD4) ; // pull-up resistor
   PCICR |= (1 << PCIE3); // Enable interrupts on PORTD (PCINT31:24)

   PCMSK0 = 0X00; // Disable unnecessary
   PCMSK1 = 0X00;
   PCMSK2 = 0X00;
   PCMSK3 |= (1 << PCINT28); // Enable  key
   sei();
}

ISR(PCINT3_vect) { // FUNCTION KEY
   uint8_t i;

   i = PORTD;
   if ((i & FUNC_SEL_KEY) > 0) { // Test a key
     LED_PORT |= (1 << PORTB0);
     _delay_ms(100);
     LED_PORT &= ~(1 << PORTB0);
     _delay_ms(300);
   }
   reti();
}


ISR(BADISR_vect) {
   LED_PORT |= (1 << PORTB0);
   _delay_ms(200);
   LED_PORT &= ~(1 << PORTB0);
   _delay_ms(200);
   LED_PORT |= (1 << PORTB0);
   _delay_ms(200);
   LED_PORT &= ~(1 << PORTB0);
   _delay_ms(200);
   LED_PORT |= (1 << PORTB0);
   _delay_ms(200);
   LED_PORT &= ~(1 << PORTB0);
   _delay_ms(200);
   reti();
}

the button has a capacitor 1uF for debouncing (together with the pull-up 
from 10 kohm)

The result is the following:

when I press the button,  are generated two flashes (instead of one),
  and when I release the button  are generated two more flashes.

Similarly, If I comment out the routine (ISR PCINT3_vect),
  the error routine (ISR BADISR_vect) generates double of the expected 
flashes.

Can anyone help me to understand the problem?

Thank you very much.


-- 
Domenico



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