MSP430FR5969: Transmit over UART using DMA

Part Number: MSP430FR5969

Tool/software:

My code sends data over UART using DMA, when a button-1 or button-2 is pressed, but it only does it once because UCA0TXIFG flag remains set even though I clear it in DMA interrupt handler. But if I insert a breakpoint inside the DMA interrupt handler before UCA0TXIFG flag is cleared, the code keeps sending data when whichever button is pressed. When I inspect the register values, without breakpoint UCATXIFG remains set in UCA0IFG register. What could be the problem? My code is basically something like below.

#include "MSPEXP430FR5969.h"
#include <string.h>

char Button_1[] = "Button 1\r\n";
char Button_2[] = "Button 2\r\n";

/**
 * main.c
 */
int main(void)
{
    WDTCTL = WDTPW | WDTHOLD;   // stop watchdog timer

    conf_gpio();
    PM5CTL0 &= ~LOCKLPM5;
    gpio_clearAllInts();

    conf_cs();
	conf_uart();
	conf_dma();
	
    __enable_interrupt();
    __delay_cycles(1000);
	enable_gpio_ints();
	enable_dma_int();

    while(1);

    return 0;
}

#pragma vector=PORT1_VECTOR
__interrupt void Port1_ISR(void)
{
    __data20_write_long( (uint32_t) &DMA0SA, (uint32_t) Button_2 );
	__data20_write_long( (uint32_t) &DMA0DA, (uint32_t) &UCA0TXBUF );
	DMA0SZ = strlen( Button_2 );
	DMA0CTL |= DMAEN;
    P1IFG &= ~BIT1;
    return;
}

#pragma vector=PORT4_VECTOR
__interrupt void Port4_ISR(void)
{
    __data20_write_long( (uint32_t) &DMA0SA, (uint32_t) Button_2 );
	__data20_write_long( (uint32_t) &DMA0DA, (uint32_t) &UCA0TXBUF );
	DMA0SZ = strlen( Button_1 );
	DMA0CTL |= DMAEN;
    P4IFG &= ~BIT5;
    return;
}

#pragma vector=DMA_VECTOR
__interrupt void DMA_ISR(void)
{
    UCA0IFG &= ~UCATXIFG; // When I insert a breakpoint here, it works properly.
}