GPRS/GSM Shield Time Setting Problems

Using Arduino Programming Questions
2

The following is how did I program it with the Serial COM.
I program the with the following code.

#include <SoftwareSerial.h>
SoftwareSerial mySerial(7, 8); // RX, TX
void setup()  
{
  Serial.begin(19200);
   // set the data rate for the SoftwareSerial port
  mySerial.begin(19200);
}
void loop() // run over and over
{
  if (mySerial.available())
    Serial.write(mySerial.read());
  if (Serial.available())
    mySerial.write(Serial.read());
}

Then I open the Serial COM tool. Program it

AT+CCLK ="12/12/27,10:49:50+08"

it returns OK,Then I program it

AT+CCLK?

it returns

+CCLK: "12/12/27,10:49:53+08"
OK

So the question is why I program the GPRS/GSM Shield with the first code, it will lost much data,And I program it through the Serial tool, the GPRS/GSM shield works fine. Is it because the Software library OVERFLOW?