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UART is repeating at output what it receives

I have a 89C5131 talking to a RS-232 device, 50 cm from the chip. Using Max232 in standard configuration and RX/TX/GND cable.

The task is to send assincronous commands to the device and read its response and ping pong the configuration.(the device timeout is 3 seconds).

Problem: For some reason (what I am asking you for help), the micro repeats - sometimes - whatever have been received at its input. Like, the micro repeats to the device the string just received. Of course the device them does not recognize it as a valid string and timeout or halts.

I use the INTSIO2 example from Keil and the following program to write and read the commands.

the code - it is sio.c with the mods below:

void com_baudrate ()
{
/*------------------------------------------------
Clear transmit interrupt and buffer.
------------------------------------------------*/
TI = 0;             /* clear transmit interrupt */
t_in = 0;           /* empty transmit buffer */
t_out = 0;

/*------------------------------------------------
Set timer 2 up as a baud rate generator.
------------------------------------------------*/
 Set_timer2_x1_mode();
  SCON = 0xF0; /* uart in mode 3 (9 bit), REN=1 */
   T2CON &= 0xF0;               /* EXEN2=0; TR2=0; C/T2#=0; CP/RL2#=0; */
   T2CON |= 0x30;               /* RCLK = 1; TCLK=1; */
   TH2=0xFF;                    /* init value */
   TL2=0xFD;                    /* init value */
   RCAP2H=0xFF;                 /* reload value, 9600 Bds at 16MHz */
   RCAP2L=0xCC;                 /* reload value, 9600 Bds at 16MHz */
        ES = 1;                                                      /* Enable serial interrupt */
        EA = 1;                                              /* Enable global interrupt */
   TR2 = 1;                     /* Timer 2 run */

}

The above is for 9600, 8, 1, even.

------------------------------------------------------------------------------*/
static void com_isr (void) interrupt 4
{
/*------------------------------------------------
Received data interrupt.
------------------------------------------------*/
if (RI != 0)
  {
  RI = 0;

  if (((r_in - r_out) & ~(RBUF_SIZE-1)) == 0)
    {
    rbuf [r_in & (RBUF_SIZE-1)] = SBUF;
    r_in++;
    }
  }

/*------------------------------------------------
Transmitted data interrupt.
------------------------------------------------*/
if (TI != 0)
  {
  TI = 0;

  if (t_in != t_out)
    {
        ACC = (tbuf [t_out & (TBUF_SIZE-1)]);
        TB8 = P;
        SBUF = (tbuf [t_out & (TBUF_SIZE-1)]);
    t_out++;
    ti_restart = 0;
    }
  else
    {
    ti_restart = 1;
    }
  }

}

This is for transmission with the even bit.

void get_serial_cmd()
{
unsigned char buff;
int counter;
        while ((buff !=0xFC) && (buff !=0))
        {
        buff = getchar();
        }
        if (buff==0xFC)
        {
                serial_read[0] = 0xFC;
                serial_read[1] = getchar();
                for (counter = 2; counter < (serial_read[1]); counter++)
                {
                serial_read[counter] = getchar();
                }
         }


}

int send_serial_cmd(unsigned char serial_cmd[16])
{
int counter;

print_to_lcd = 0;       //Diverts putchar to UART
for (counter = 0; counter<serial_cmd[1]; counter++)
    {
        putchar(serial_cmd[counter]);
    }
print_to_lcd = 0;       //Diverts putchar to LCD
return (0);
}

The above receives and sends the strings from the device.

The program calls this function as:

void action_bill_accepted()
{

        if (serial_read[2] == 0x15)
                {

                send_serial_cmd(ACKNOWLEDGE);
                get_serial_cmd();
                }
        if (serial_read[2] == 0x16)
                {
                send_serial_cmd(STATUS_REQUEST);
                get_serial_cmd();
                }

}

_getkey and putchar are below:

char _getkey (void)
{
int k;
do
  {
    k = com_getchar();
  }
while (k == -1);

return ((unsigned char) k);
}

char putchar (char c)
{
        volatile unsigned int i;
        if (print_to_lcd == 1)
        {
                lcd_putchar(c);
        }
        if (print_to_lcd == 0)
        {
        while (com_putchar (c) != 0)
        {
                for (i=0; i<1000; i++)
            {
                //*** DO NOTHING **
            }
        }
        }

return(c);
}

Any suggestion is welcome.