I honestly don't think it works in such a manner. I think the range has to be lowest to highest, for it to work.
CASE 11 TO 16 rather than 16 TO 11.
Try reversing those limits and see if it fixes the issue.
Looks like your right, though why it cares?
perhaps I have gotten to used to be able to go high to low in things like LINE and _PUTIMAGE?
and it doesn't care if I CASE 16,15,14,13,12,11.
but what ever, found why there was an issue and resolved,
Thanks Steve.