UART 7bits trouble

Hi everyone,

When I program UART 8bit, I can debug data in Received Interrupt Routine, I changed it to UART 7 bits as below, seem no data came in the ISR.

UCA0CTL0 |= UCMODE_0 + UC7BIT ;

I made a beakpoint in the received interrupt rountine, It's never jump to this point in 7 bits mode. In 8 bits is fine.

I think the ISR can not detect the coming data. I wonder about what is my omissions.
The discrepancy between 7 bits and 8 bits only the above config. I also changed to 7 bits mode in Serial Port Terminal program to send 7 bits data.