Questions about using the P1.1

Dear！

We got a problem when using the MCU MSP430F67791A(100-Pin PZ Package)，we set P1.1 as digital input, the detail of the problem is as follows:

1、Originally, the initial code of P1.1 was:

P1SEL0 &= ~BIT1; /*choose P1.1 as I/O function*/
P1DIR &= ~BIT1; /*set P1.1 as input*/

When we using multimeter to mesure the voltage of P1.1, the result was 3.25V, so the state should be 1,
but when we observing the value of P1IN1 via IAR Embedded Workbench, the result was 0， it was not right.

2、Subsequently, we modified the initial code of P1.1:
P1SEL0 &= ~BIT1; /*choose P1.1 as I/O function*/
P1DIR |= BIT1; /*Firstly set P1.1's direction as output */
DELAY_4uS();
P1OUT &= ~BIT1; /*output 0*/
DELAY_4uS();
P1DIR &= ~BIT1; /*Finally，set P1.1's direction as input*/

When we using multimeter to mesure the voltage of P1.1, the result was still 3.25V,
when we observing the value of P1IN1 via IAR Embedded Workbench, the result was 1， it was right.

3、We also use other PINs(such as P1.4) as digital input，the initial code of P1.4 was:
P1SEL0 &= ~BIT4; /*as I/O function*/
P1DIR &= ~BIT4; /*as input*/

When we using multimeter to mesure the voltage of P1.4, the result was 3.25V, so the state was 1,
when we observing the value of P1IN4 via IAR Embedded Workbench, the result was 1， it was right.
Could you please help us to analysis why P1.1 is different from others?

Thanks!