Project using SoftwareSerial, works with Olimexino 328, not with UNO

Hi. I have a setup where I have an XBEE coordinator transmitting the string “REQ_COORD\n” every two seconds. An XBEE router is connected to an Arduino on pins 10 and 11, and the Arduino is programmed to create a SoftwareSerial port on those pins (10 and 11) and print what it sees to the hardware Serial port (pins 0 and 1). I then use the Arduino software’s Serial Monitor to observe output. The program outputs each character in the SoftwareSerial buffer, followed by its ASCII decimal code.

The Arduino code is then:

#include <SoftwareSerial.h>

SoftwareSerial softSerial(11,10);
char c; // Holds the character read from serial/software serial
int i; // Holds ASCII value of character read

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

void loop()
{
  if(softSerial.available() > 0) //Prints character and ASCII code in SoftwareSerial buffer.
  {
    Serial.println("Software Serial:");
    while(softSerial.available() > 0)
    {
      c = softSerial.read();
      i = (int)c;
    
      Serial.print(c);
      Serial.print(" ");
      Serial.println(i);
    }
  }
}

Typical output when the program is uploaded to an Arduino UNO is:

Software Serial:
 0
 0
 0
 0
 0
 0
 0
 0
 0
 0
Software Serial:
 0
 0
 0
 0
 0
 0
 0
 0
 0
 0
 0
Software Serial:
 0
Software Serial:
 0
Software Serial:

As we can see, the bytes being read by SoftwareSerial.read() are all null characters (ASCII code 0).

However, when I upload the code to an Olimexino-328 (an Arduino derivative that is programmed as “Arduino Duemilanove w/ ATMEGA 328”), the output is:

Software Serial:
R 82
E 69
Q 81
_ 95
C 67
O 79
O 79
R 82
D 68

 13

 10
Software Serial:
R 82
E 69
Q 81
_ 95
C 67
O 79
O 79
R 82
D 68

 13

 10

i.e. exactly what you’d expect. So why does SoftwareSerial not work as expected on the Arduino UNO? The only caveat I could find for SoftwareSerial is this:

Not all pins on the Mega and Mega 2560 support change interrupts, so only the following can be used for RX: 10, 11, 12, 13, 14, 15, 50, 51, 52, 53, A8 (62), A9 (63), A10 (64), A11 (65), A12 (66), A13 (67), A14 (68), A15 (69)