Interrupt program exception

The function uipInterruptServiceEngine（） is the RTOS's interrupt handler function.

In this project, I just use TIM1 update interrupt, and since the program jump into function uinInterruptServiceEngine()(in MSP Stack). Some times, the program will run in the step: 

1: uip_KERNEL_DISABLE_INTS.

2: if (uipSystemMode != uip_KERNEL_RUNNING) 

3:uipScheduler()

Just jump from sentence (uipSchedulerLock != 0) to uipScheduler(), without implement uipGetNextTask() and if (((uipCurrentTaskTCBPtr -> uipTaskState) & uip_TASK_STATE_MASK) == RUNNING_STATE ), why this happend?

VOID uipInterruptServiceEngine(VOID)
{
    /*disable interrrupt*/
    uip_KERNEL_DISABLE_INTS;
	
    ...................

    if (uipSchedulerLock != 0) {
        
        /* Restore original sys-int-ctrl value */
        uip_KERNEL_RESTORE_INTS;
      
        return;
    }
    
    uipGetNextTask();
    
    if (uipNextRunningTaskTCBPtr == uipCurrentTaskTCBPtr) {        

        ..................

        return;            
    } 
	
    if (((uipCurrentTaskTCBPtr -> uipTaskState) & uip_TASK_STATE_MASK) == RUNNING_STATE )
    {
        uipCurrentTaskTCBPtr -> uipTaskState &= uip_TASK_EXTENDED;
        uipCurrentTaskTCBPtr -> uipTaskState |= READY_STATE;      
    } 
        
    uipScheduler();
    
    /* Restore original sys-int-ctrl value */
    uip_KERNEL_RESTORE_INTS;
    
}