OneWire DS18B20 on mighty 1284p can't find my sensors, same sensors work w/ Duemilanove

OneWire DS18B20 on mighty 1284p can't find my sensors, same sensors work w/ Duemilanove

I have uploaded the DS18x20 Temperature example sketch (unaltered, except I tried multiple pins for the I2C communication) to my proven Duemilanove and my mighty 1284p.
On the Duemilanove my two DS18B20 temperature sensors are found and read correctly:
ROM = 28 36 6D 51 4 0 0 75
  Chip = DS18B20
  Data = 1 D6 1 4B 46 7F FF A 10 43  CRC=43
  Temperature = 29.37 Celsius, 84.87 Fahrenheit
ROM = 28 19 6 51 4 0 0 86
  Chip = DS18B20
  Data = 1 A7 1 4B 46 7F FF 9 10 E0  CRC=E0
  Temperature = 26.44 Celsius, 79.59 Fahrenheit
No more addresses.
(...)
Whereas the 1284p only says
No more addresses.

No more addresses.

(...)
I have not changed the wiring of the sensors; they are connected +5/GND, Data is pulled to +5V with a 2k7 and also to the reading pin, respectively. I have tested multiple pins for I2C communication - they all work on the Duemilanove, none work on the 1284p.
I am assuming some issues with I2C with mighty 1284p, but maybe someone else has another idea.
Here's the code (the unchanged example sketch, I have been taught to "include the used code, always!", so here it is):
#include <OneWire.h>

// OneWire DS18S20, DS18B20, DS1822 Temperature Example
//
// http://www.pjrc.com/teensy/td_libs_OneWire.html
//
// The DallasTemperature library can do all this work for you!
// http://milesburton.com/Dallas_Temperature_Control_Library

OneWire  ds(0);  // on pin 10

void setup(void) {
  Serial.begin(9600);
}

void loop(void) {
  byte i;
  byte present = 0;
  byte type_s;
  byte data[12];
  byte addr[8];
  float celsius, fahrenheit;

  if ( !ds.search(addr)) {
    Serial.println("No more addresses.");
    Serial.println();
    ds.reset_search();
    delay(250);
    return;
  }

  Serial.print("ROM =");
  for( i = 0; i < 8; i++) {
    Serial.write(' ');
    Serial.print(addr[i], HEX);
  }

  if (OneWire::crc8(addr, 7) != addr[7]) {
      Serial.println("CRC is not valid!");
      return;
  }
  Serial.println();

  // the first ROM byte indicates which chip
  switch (addr[0]) {
    case 0x10:
      Serial.println("  Chip = DS18S20");  // or old DS1820
      type_s = 1;
      break;
    case 0x28:
      Serial.println("  Chip = DS18B20");
      type_s = 0;
      break;
    case 0x22:
      Serial.println("  Chip = DS1822");
      type_s = 0;
      break;
    default:
      Serial.println("Device is not a DS18x20 family device.");
      return;
  }

  ds.reset();
  ds.select(addr);
  ds.write(0x44,1);         // start conversion, with parasite power on at the end

  delay(1000);     // maybe 750ms is enough, maybe not
  // we might do a ds.depower() here, but the reset will take care of it.

  present = ds.reset();
  ds.select(addr);   
  ds.write(0xBE);         // Read Scratchpad

  Serial.print("  Data = ");
  Serial.print(present,HEX);
  Serial.print(" ");
  for ( i = 0; i < 9; i++) {           // we need 9 bytes
    data[i] = ds.read();
    Serial.print(data[i], HEX);
    Serial.print(" ");
  }
  Serial.print(" CRC=");
  Serial.print(OneWire::crc8(data, 8), HEX);
  Serial.println();

  // convert the data to actual temperature

  unsigned int raw = (data[1] << 8) | data[0];
  if