XDOFX Functions in RTF Template

I am creating a template where an XML value (LABELNUM in my example below) is incremented and printed three times, like this:

<?LABELNUM?>

<?xdofx:lpad(to_char(LABELNUM+1),6,'0')?>

<?xdofx:lpad(to_char(LABELNUM+2),6,'0')?>

If the initial value of LABELNUM is 000001, then the output is simply:

000001

000002

000003

This is working perfectly well.

Right below the printed LABELNUM, I am also creating a barcode with the same data, like this:

<?LABELNUM?>

<?format-barcode:LABELNUM;'code128a';'XMLPBarVendor'?>

The above also works great.  So far so good.

The problem is when I try to the print the other two barcodes with the incremented value. This is what I am trying, but it is not working: