isr_evt_set problem

Hi, All!

My problem is exactly the same as http://www.keil.com/forum/13634/

void UARTHandler (void) __irq {
   isr_evt_set(0x0001,UART_TASK);
  //use "os_evt_set" works
}


void task_UART_received (void) __task  {
   for(;;) {
      //can not get here if I use "isr_evt_set":

      os_evt_wait_or(0x0001,0xffff);
      ......
   }
}

I could not reach os_evt_wait_or section, program is always pending in irq interrupt.
But if I change isr_evt_set to os_evt_set everything work fine.

Task task_UART_received is created before first UART interrupt occurs.
I don't understand where error is.
Do you have some ideas about? Thank you.