CC3200: uart dma interrupt flag cannot be clear

Dear Ti's engineer

In my code i want to send frames by the DMA , when the dma Tx done it raise the DMATXMIS flag in the register of UARTMIS. Then in the uart isr function i clear the flag by write 1 to the DMATXIC bit in the UARTTICR register., but i found that  the DMATXMIS flag is not be cleared. This is different with the description in the cc3200 user manual.  Below is my testing code, where ZIGBEECOMM is uart1

static void uartslkIsr(void)

{

unsigned long uiIntStat,i;

uiIntStat = MAP_UARTIntStatus(ZIGBEECOMM, 1);

       /*DMA Tx done interrupt*/
       if(uiIntStat & 0x00020000){
         MAP_UARTIntClear(ZIGBEECOMM, 0x00020000);
         i = MAP_UARTIntStatus(ZIGBEECOMM, 1);
         xSemaphoreGiveFromISR(waitUntilSendDone, &xHigherPriorityTaskWoken);
       }

      }