MSP430F5510 I2C on port 4

I took the TI example for I2C "uscib0_i2c_08 and tried to convert it to use Port 4.  It has a problem where it goes into the interrupt and sets the first bit but after that it hangs (goes back to the main loop and no more interrupts are sent).  Here is the code:

#include <msp430.h>

unsigned char *PTxData;                     // Pointer to TX data
unsigned char TXByteCtr;

const unsigned char TxData[] =              // Table of data to transmit
{
  0x18,  // reg = timer control
  0x2  // data
};

int main(void)
{
  unsigned int i;

  WDTCTL = WDTPW + WDTHOLD;                 // Stop WDT


  PJDIR |= 0x02;                             // PJ.1 RTC switch
  PJOUT = 0x0;                                // RTC switch low = RTC on


  P4SEL = 0x06;
  P4DIR  |= 0x06;


  PMAPPWD  = 0x02D52;                        // Enable Write-access to modify port mapping registers
  PMAPCTL |= PMAPRECFG;
  P4MAP1 = PM_UCB1SDA;
  P4MAP2 = PM_UCB1SCL;
  PMAPPWD  = 0;                              // Disable Write-Access to modify port mapping registers





  UCB1CTL1 |= UCSWRST;                      // Enable SW reset
  UCB1CTL0 = UCMST + UCMODE_3 + UCSYNC;     // I2C Master, synchronous mode
  UCB1CTL1 = UCSSEL_2 + UCSWRST;            // Use SMCLK, keep SW reset
  UCB1BR0 = 12;                             // fSCL = SMCLK/12 = ~100kHz
  UCB1BR1 = 0;
  UCB1I2CSA = 0xD2;                         // Slave Address is 0D2h = RTC
  UCB1CTL1 &= ~UCSWRST;                     // Clear SW reset, resume operation
  UCB1IE |= UCTXIE;                         // Enable TX interrupt

  while (1)
  {
    for(i=0;i<10;i++);                      // Delay required between transaction
    PTxData = (unsigned char *)TxData;      // TX array start address
                                            // Place breakpoint here to see each
                                            // transmit operation.
    TXByteCtr = sizeof TxData;              // Load TX byte counter

    UCB1CTL1 |= UCTR + UCTXSTT;             // I2C TX, start condition
    
     __bis_SR_register(LPM0_bits + GIE);     // Enter LPM0, enable interrupts
    __no_operation();                       // Remain in LPM0 until all data
                                            // is TX'd
    while (UCB1CTL1 & UCTXSTP);             // Ensure stop condition got sent
  }
}

//------------------------------------------------------------------------------
// The USCIAB1TX_ISR is structured such that it can be used to transmit any
// number of bytes by pre-loading TXByteCtr with the byte count. Also, TXData
// points to the next byte to transmit.
//------------------------------------------------------------------------------
#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector = USCI_B1_VECTOR
__interrupt void USCI_B1_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(USCI_B1_VECTOR))) USCI_B1_ISR (void)
#else
#error Compiler not supported!
#endif
{
  switch(__even_in_range(UCB1IV,12))
  {
  case  0: break;                           // Vector  0: No interrupts
  case  2: break;                           // Vector  2: ALIFG
  case  4: break;                           // Vector  4: NACKIFG
  case  6: break;                           // Vector  6: STTIFG
  case  8: break;                           // Vector  8: STPIFG
  case 10: break;                           // Vector 10: RXIFG
  case 12:                                  // Vector 12: TXIFG  
    if (TXByteCtr)                          // Check TX byte counter
    {
      UCB1TXBUF = *PTxData++;               // Load TX buffer
      TXByteCtr--;                          // Decrement TX byte counter
    }
    else
    {
      UCB1CTL1 |= UCTXSTP;                  // I2C stop condition
      UCB1IFG &= ~UCTXIFG;                  // Clear USCI_B1 TX int flag
      __bic_SR_register_on_exit(LPM0_bits); // Exit LPM0
    }  
  default: break;
  }
}