SSI3 on EK-TM4C123GXL changes behavior of the PB6, PB7 pins

SSIConfigSetExpClk(SSI3_BASE, CLOCK_RATE, SSI_FRF_MOTO_MODE_3,SSI_MODE_MASTER, 1200000,16);

void initSPI3(void)
{   
    // attach spi master to SSI3
    SysCtlPeripheralEnable(SYSCTL_PERIPH_SSI3);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOD);

    /*
     * Configure the appropriate pins to be SSI instead of GPIO. The FSS (CS)
     * signal is directly driven
     */
    GPIOPinConfigure(GPIO_PD0_SSI3CLK);
    GPIOPinConfigure(GPIO_PD2_SSI3RX);
    GPIOPinConfigure(GPIO_PD3_SSI3TX);
    GPIOPinConfigure(GPIO_PD1_SSI3FSS);
    GPIOPinTypeSSI(GPIO_PORTD_BASE, GPIO_PIN_3| GPIO_PIN_2| GPIO_PIN_0);
    GPIOPinTypeGPIOOutput(GPIO_PORTD_BASE, GPIO_PIN_1);  
      
    /*
     * Set the SSI output pins to 4MA drive strength and engage the
     * pull-up on the receive line.
     */
    
    GPIOPadConfigSet(GPIO_PORTD_BASE, GPIO_PIN_2, GPIO_STRENGTH_4MA,
                         GPIO_PIN_TYPE_STD_WPU);
    GPIOPadConfigSet(GPIO_PORTD_BASE, GPIO_PIN_0| GPIO_PIN_3| GPIO_PIN_1,
                         GPIO_STRENGTH_8MA, GPIO_PIN_TYPE_STD);
    
    // Configure the SSI3 port for mode 3, 16 bit data
    SSIConfigSetExpClk(SSI3_BASE, CLOCK_RATE, SSI_FRF_MOTO_MODE_3,SSI_MODE_MASTER, 1200000,16);
    SSIEnable(SSI3_BASE);
}