Interrupt based timer outputting wrong frequency

This object of the test program below is to toggle a LED at a 5 hz frequency. When the actual 12F1822 test circuit is run, the LED toggles at a 50 hz rate, confirmed by oscilloscope.

What seems to be happening is that the increment-to-count 10 part of the handler is not executing. The toggle frequency is determined only by the pre-scale and post- scale settings. Any ideas?

Code:

---

***************************************
*Program to test timer 2 interrupt                                     
*Target processor is PIC 12f1822                                       
*88 program words, revised 09/26/2011                                   
***************************************
'set 12f1822 configurat1on
#CONFIG
  __config _CONFIG1, _FOSC_INTOSC & _MCLRE_OFF & _CLKOUTEN_OFF
  __config _CONFIG2, _PLLEN_OFF & _LVP_OFF
#ENDCONFIG 

'set registers
  OSCCON = 01101000  '4 mhz osc
  OSCTUNE = 0          'factory calibration
  ANSELA = 0            'all digital
  OPTION_REG.7 = 0  'global pullups enabled
  WPUA = 000100          'porta pin2 weak pullup enabled
  CM1CON0.7 = 0      'comparator disabled
  TRISA  = 001111      'porta.5 and porta.4 are outputs, all others input

  INTCON = 11000000    'global and peripheral interrupts enabled
  PIE1 = 00000010        'enable tmr2 interrupt
  T2CON = 00011110    'turn on tmr 2 (bit 2),1:16 prescale,1:4 postscale
  PIR1.1 = 0            'clear tmr2 interrupt flag
  PR2 = 156            'preset for 100 hz interrupt

    define INTHAND clock

goto overint

asm
clock
  INCF  _ticks,f        ;ticks=ticks + 1
  MOVF  _ticks,w      ;read ticks into w
  SUBLW  d'10'          ;subtract w from decimal 10
  BTFSS  STATUS,2  ;zero?
  RETFIE                  ;return for next interrupt if not zero
  CLRF  _ticks          ;clear ticks count

  MOVLW  b'00010000  ;load binary literal into w
  XORWF  PORTA,f      ;toggle porta pin4
  BSF  _tenths          ;set tenths-changed flag
  BCF    PIR1,1          ;reset tmr2 interrupt flag
  RETFIE                  ;return to main
endasm

overint:

'declare variables
        ticks    var byte bank0
        tenths  var bit  bank0

'initialize register functions
        porta.4  = 1          'initialize led off
        tenths = 0            'clear tenths-changed bit

main: 
  tenths = 0                  'clear tenths-changed bit
  pause 1000                'wait 1 second
goto main                    'loop back to main

---

In the first part of the ISR, it doesn't clear the interrupt flag if the value isn't 10.
So it exits and re-enters the ISR 10 times really fast.

Once it gets to 10, it toggles the pin and finally clears the flag, which all happens from a single interrupt.

Darrel,
Thanks, it's working now ... getting 5 hz toggle. Added this line at the beginning of the ISR routine:

BCF PIR1,1 ;clear tmr2 interrupt flag