Problem with ASM IRQ using FSR0 on PIC18F252

[mytekcontrols]

I have a 6 digit counter routine incorporated as an ASM IRQ on a PIC18F252 under MEL PicBasic Pro. It utilizes in-direct addressing of a 6 byte array to update and store the counter's count. The problem is that the part of the routine that is supposed to clear a digit as it rolls over from 9 doesn't always work. Here is the partial code showing only the UP counting module:

DEFINE INTHAND myint

Ecount     var   byte[6] bankA
fsave	    var   word  bankA  system
loopcount var   byte

Goto Start     ' jump past interrupt routine

;================================================
asm
myint
; save the FSR value because it gets changed below
    movf	Low FSR0, W
    movwf      fsave
    movf	High FSR0, W
    movwf      fsave+1

;-------------------------------------------------------
;polling and calling routine for counter
;-------------------------------------------------------

; (code not shown)

;-------------------------------------------------------
;6 digit count up module - each entry increments counter
;-------------------------------------------------------

countup
    clrf   _loopcount

;set base address of array
    movlw	Low _Ecount
    movwf	FSR0L
    movlw	High _Ecount
    movwf	FSR0H

inc_loop
    movlw  d'9'
    subwf  INDF0,W
    btfsc  STATUS, Z          ; Have we hit top for this digit?
    goto   nextdigit             ; Yes, go to next! 
    incf   INDF0,F               ; else keep incrementing it, and...
    goto   restore               ; leave!
nextdigit
    clrf   POSTINC0             ; (clear INDF and increment FSR)
    incf   _loopcount,F
    movlw  d'6'
    subwf  _loopcount,W
    btfss  STATUS, Z          ; Have we checked all 6 digits?
    goto   inc_loop             ; No go to next!

;restore registers
restore
    movf	fsave, W
    movwf	Low FSR0
    movf	fsave+1, W
    movwf	High FSR0
    retfie  FAST
endasm
;================================================

Start:
;-------------------------------------------------------
;PBP interrupt init and counter display
;-------------------------------------------------------

; (code not shown)

End

The problem when it manifests is that a given digit will continue to increment beyond the number 9. It is as if the array byte pointed to by the FSR has changed momentarily, thereby missing the check for zero after subtracting 9.

Is code generated by PBP able to interfere with the in-direct addressing? The reason I ask this is, that I originally coded the counter routine without using FSR and instead used Ecount+1, Ecount+2, ect. to access the array. I achieved reliable counting using this method, although at the cost of considerably more code.

The problem is very intermittent with the FSR routine. So this too tends to point to outside influences causing the glitch. Has anyone else encountered such a problem when using SR's and interrupts under PBP?