MSP430F2274: Master continuously receives data although it is not connected to slave or is actually receiving data

#include <msp430.h>

void configGPIO(void);
void configSPI(void);

unsigned char send_byte;

int main(void)
{
    volatile int i;

    WDTCTL = WDTPW + WDTHOLD;               // Stop watchdog timer
    configGPIO();
    configSPI();

    P3OUT &= ~0x01;                         //clear output of reset/enable
    P3OUT |= 0x01;                          //set output to high

    for(i = 50; i > 0; i--);

    send_byte = 0x01;
    UCB0TXBUF = send_byte;

    __bis_SR_register(LPM0_bits + GIE);     //enter low power mode 3 w/interrupts enabled

}

void configGPIO(void)
{
    /* configure ports for USCI B0 SPI mode */
    P1OUT = 0x00;                  //setup for LED output
    P1DIR |= 0x03;                  //

    P3OUT = 0x01;                   //set output to high
    P3DIR |= 0x01;                  //output direction for rst/enable
    P3SEL |= 0x0E;                  //slave out/master in, clock input/output
}


void configSPI(void)
{
    /* configure USCI B0 for SPI mode */
    UCB0CTL0 |= UCCKPL + UCMSB + UCMST + UCSYNC;     //msb first, master mode, 3-pin SPI
    UCB0CTL1 |= UCSSEL_2;
    UCB0BR0 |= 0x02;
    UCB0BR1 |= 0x00;
    UCB0CTL1 &= ~UCSWRST;                   //initialize USCI state machine
    IE2 |= UCB0RXIE;             //enable rx/tx interrupts
}


#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=USCIAB0RX_VECTOR
__interrupt void USCIB0RX_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(USCIAB0RX_VECTOR))) USCIA0RX_ISR (void)
#else
#error Compiler not supported!
#endif
{
    volatile int j;
    volatile long g;
    while (!(IFG2 & UCB0TXIFG));


    volatile int junk = UCB0RXBUF;
    //P1OUT ^= 0x02;
    for(g = 50000; g > 0; g--);
    P1OUT ^= 0x02;

    send_byte++;
    UCB0TXBUF = send_byte;

    //IE2 &= ~UCB0RXIE;

    for(j = 50; j > 0; j--);
}