CCS/TM4C1294NCPDT: TM4C1294 UARTCharsAvail can't check 1byte

I try to read only 1 byte from UART with the Interrupt, however, somehow while(UARTCharsAvail(UART0_BASE)) do not return true if the I'm not send 4 bytes. Is while(UARTCharsAvail(UART0_BASE)) only return true if the Receive FIFO have 32-bits data in it?
I try to send only 1 byte from PC to the UART. But somehow I can't read that byte unless I send 4 times. Is there any way I can just read 1 byte before I can do anything else?

Best regards,

void UARTIntHander(void){

    uint32_t ui32Status;
    uint8_t data = 0;
    //
    // Get the interrrupt status.
    //
    ui32Status = UARTIntStatus(UART0_BASE, true);

    //
    // Clear the asserted interrupts.
    //
    UARTIntClear(UART0_BASE, ui32Status); // clear the asserted interrupts

    //
    // Loop while there are characters in the receive FIFO.
    //
    while(UARTCharsAvail(UART0_BASE)) // loop while there are chars // return if 32 bit is full.
    {
        data = UARTCharGetNonBlocking(UART0_BASE);
        UARTCharPutNonBlocking(UART0_BASE, data); //echo character
    }

}




void
InitConsole(void)
{
    IntMasterEnable();


    SysCtlPeripheralEnable(SYSCTL_PERIPH_UART0);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA);

    GPIOPinConfigure(GPIO_PA0_U0RX);
    GPIOPinConfigure(GPIO_PA1_U0TX);

    UARTClockSourceSet(UART0_BASE, UART_CLOCK_PIOSC);

    GPIOPinTypeUART(GPIO_PORTA_BASE, GPIO_PIN_0 | GPIO_PIN_1);

    UARTStdioConfig(0, 115200, ui32SysClockFreq);

    // For interrupt

    IntEnable(INT_UART0);
    UARTIntEnable(UART0_BASE, UART_INT_RX); // trigger only in RX

    //UARTIntEnable(UART0_BASE, UART_INT_RX | UART_INT_RT);

    UARTFIFODisable(UART0_BASE); // Clear FIFO
    UARTFIFOEnable(UART0_BASE);

}