strange problem during frequency measurement.

flag1 = read_eeprom(FLAG_ADDRESS);    
write_eeprom(FLAG_ADDRESS,flag);

#include "18f2520.h"
#fuses H4, NOWDT               
#use delay(clock=16000000)         // 4Mhz crystal with PLL enabled. 4Mhz * 4 => 16Mhz 

#define     output_pin    PIN_A4
#define  	LED  		  PIN_C4

#define FLAG_ADDRESS 		10
#define FLAG_STATUS_ADDRESS     20

int8 old_f, f = 0;
int16 temp_data; 
int32 local;
int8 HIGH;

int8 flag1;

int16 isr_ccp_value;
int16 current_ccp_value; 
int32 frequency; 
int flag;

#int_ccp1
void ccp1_isr(void)
{
	int16 current_ccp;
	static int16 old_ccp = 0;
	f++; 	
	current_ccp = CCP_1;   // Read the 16-bit hardware CCP1 register 
	
	isr_ccp_value = current_ccp - old_ccp;       
	                              
	old_ccp = current_ccp;        // Save the current ccp value for the next pass.

}

void main()
{
set_tris_a(0x00);
set_tris_c(0x00);

set_timer1(0);                               //   Timer value to 0
setup_timer_1(T1_INTERNAL | T1_DIV_BY_1);    //   Timer1 internal & 1:1 Prescaler
setup_ccp1(CCP_CAPTURE_RE);                  //   Looks for Rising edge

clear_interrupt(INT_CCP1);                  //   disables the CCP1 interrupt
enable_interrupts(INT_CCP1);                //   enables the CCP1 Interupt
enable_interrupts(GLOBAL);                  //   Enables global interrupt

HIGH = 1;

while(1)
{   
current_ccp_value = isr_ccp_value;         
enable_interrupts(GLOBAL);           		 //   enable interrupts

	while(old_f == f);
	old_f = f;
	if(f < 64)
	   {

	       do
	       {
 	         temp_data=current_ccp_value;
	       } while (current_ccp_value!=temp_data);
	       local += temp_data;   
	   }
	else
	   {

    	disable_interrupts(GLOBAL);						
		frequency = (int16)((640 * 393822) / (local));       	

	if((frequency < 2000))     
	{
		output_high(LED);
		output_high(output_pin);                           
		flag = 1;                                                  
	}

	flag1 = read_eeprom(FLAG_ADDRESS);                // read the value in eeprom address - flag
	
	if((frequency > 2000) && (frequency < 3000) && (flag1 == 1))   
	{
		output_high(LED);
		output_high(output_pin);                          
		flag = 1;                                                      
	}

	if((frequency > 3000))       
	{
		output_low(LED);
		output_low(output_pin);                          
		flag = 0;                                                      
	}

	if((frequency > 2000) && (frequency < 3000) && (flag == 0))  
	{
		output_low(LED);
		output_low(output_pin);
		flag = 0;                                        
	} 

    write_eeprom(FLAG_ADDRESS,flag); 	
	local = f=old_f=0;	
	}
}
}