CCS/CC2640: CC2640 Task_sleep() not working as expected w/o JTAG?

Part Number:CC2640

Tool/software: Code Composer Studio

Hello , 

Recently , I found our code to failed to delay by calling Task_sleep() . 

For example ,  tring to have a delay for 9 seconds  by 

either

          Task_sleep (9*ONE_SECOND) ;

or 

int i ; 

for (i=0;i<9;i++) 

 Task_sleep (ONE_SECOND) ;

The code works fine when JTAG connected for debug . However , if we remove JTAG connection , let the system run . The delay will much shorter then 9 seconds .

Any suggestions ?

PS. Our CLOCK shall be fine because we have another task controlling LED blinking , and it's works fine . 

Best regards,

Sidney