BBB Fseek weirdness

    // Now output a value to it
    pFile = fopen("/sys/class/gpio/gpio30/value","w");
    if (pFile == NULL) {
        printf("Cannot open /sys/class/gpio/gpio30/value to write to the GPIO\n");
        exit(1);
    }
    int i;
    for (i=0; i < 10; i++) {
        fseek(pFile, 0, SEEK_SET);
        result = fprintf( pFile, "0" );
        if (result < 0) {
            printf("Cannot write to /sys/class/gpio/gpio30/value to set GPIO\n");
            fclose(pFile);
            exit(1);
        }
        usleep(500);
        fseek(pFile, 0, SEEK_SET);
        result = fprintf( pFile, "1" );
        if (result < 0) {
            printf("Cannot write to /sys/class/gpio/gpio30/value to set GPIO\n");
            fclose(pFile);
            exit(1);
        }
        usleep(500);
// Adding this extra code screws up the high pulses
//        fseek(pFile, 0, SEEK_SET);
//        result = fprintf( pFile, "0" );
//        if (result < 0) {
//            printf("Cannot write to /sys/class/gpio/gpio30/value to set GPIO\n");
//            fclose(pFile);
//            exit(1);
//        }

    }

    fclose(pFile);