Led toggling more quickly when oscillator pending flag is not reset.

Hai everyone.
 

 I am beginner in MSP430, I was watching MSP430 wprkshop videos from Texas Instruments.
 I was following the steps and the code they explained in workshop in one code where they source clock from VLO and toggle led, I forgot to reset oscillator pending interrupt flag then led started blinking fastly can anyone explain me why.
 

 Here is the code snippet.
 

 #include <msp430g2553.h>

 #ifndef TIMER0_A1_VECTOR
 #define TIMER0_A1_VECTOR TIMERA1_VECTOR
 #define TIMER0_A0_VECTOR TIMERA0_VECTOR
 #endif
 

 void main(void) {
     WDTCTL = WDTPW | WDTHOLD; // Stop watchdog timer
 

 P1DIR = 0x40; //Configure P1.6 as output by writing 1 to corresponding pin
 P1OUT = 0; //make output of that pin as zero
 
 BCSCTL3 |= LFXT1S_2; //Configure basic clock system+ to use VLO
 //IFG1 &= ~OFIFG;        //I forgot to add this line in the code, Disabling Oscillator interrupt                                                                    //pending flag then LED started blinking fastly
 _bis_SR_register(SCG0+SCG1);
 BCSCTL2 |= SELM_3 + DIVM_3;
 

 while(1)
 {
 P1OUT = 0x40; // LED on
 _delay_cycles(100);
 P1OUT = 0; // LED off
 _delay_cycles(5000);
 }
 }