Using the same library twice?

Projects Programming
4 
#include <SD.h>

byte SDSS2 = 5;  // Slave Select pin for second SD card.
SDClass SD2;

void setup() {
  SD.begin();
  SD2.begin(SDSS2);
}

void loop() {
}

The library creates one instance (named 'SD') but doesn't seem to mind users creating more. I don't know if the library will work properly if you do this.