Thanks Heckler, I have done something similar after Googling the problem,
but since the device is in a car, I can't test it every time I change something,
and tend to wait till I'm driving anyway.

The ISR has RB0 trigger as a possible source as well. I have tried this:

Code:
intsync = 0
LCDOUT $FE,2                                    'VFD cursor return home
FOR gcnt = 0 TO 39                                'print data to vfd
LCDOUT vfd[gcnt]                                '
NEXT gcnt                                        '
'
if intsync = 1 THEN                                '
intsync = 0                                        '
LCDOUT $FE,2                                    'VFD cursor return home
FOR gcnt = 0 TO 39                                'print data to vfd
LCDOUT vfd[gcnt]                                '
NEXT gcnt                                        '
endif                                            '
'
if intsync = 1 THEN                                '
LCDOUT $FE,2                                    'VFD cursor return home
FOR gcnt = 0 TO 39                                'print data to vfd
LCDOUT vfd[gcnt]                                '
NEXT gcnt                                        '
endif                                            '
40 char, single line display.
The ISR sets the status of intsync.
Fingers crossed