Confusion about info in LPC4074 header file...

In the 2012-04-25 version of the LPC407x_8x_177x_8x.h that came with my recent download of
the MDK ARM tools I discovered something odd about the definitions of some fields for the
UART type definitions. Specifically, for UART types 0 and 1 the transmit holding register is
an 8-bit value, but for UART type 4 it's a 32-bit value. I don't see any difference in the
datasheet for these registers. The difference caused an issue for when creating a class member
variable that pointed to this register; or rather, when assigning values to it using the
header file.

For reference, this variables were declared in my class,

volatile uint8_t * pTHR;  // ptr to MCU UART transmit holding register
volatile uint32_t * pIER; // ptr to MCU UART interrupt enable register

but to make the compiler happy I had to do this in setup code for this class.

        // save values needed for ISR and read/write methods
        if(info->comport==0){
                nIntNum=UART0_IRQn;
                pTHR = &LPC_UART0->THR;
                pIER = &LPC_UART0->IER;
        }else if(info->comport==1){
                nIntNum=UART1_IRQn;
                pTHR = &LPC_UART1->THR;
                pIER = &LPC_UART1->IER;
        }else if(info->comport==2){
                nIntNum=UART2_IRQn;
                pTHR = &LPC_UART2->THR;
                pIER = &LPC_UART2->IER;
        }else if(info->comport==3){
                nIntNum=UART3_IRQn;
                pTHR = &LPC_UART3->THR;
                pIER = &LPC_UART3->IER;
        }else if(info->comport==4){
                nIntNum=UART4_IRQn;
                // This THR is defined differently in the KEIL supplied header, but not the data sheet.
                // Not sure why that is.  You can only write 8-bit values to the THR.
                pTHR = (volatile uint8_t *)&LPC_UART4->THR;
                pIER = &LPC_UART4->IER;
        }else{
                return false;
        }

Can anyone tell me why the THR for UART4 is defined as a 32-bit value,
but all other UART THRs are defined as 8-bit values?

Thanks.