DonCaron: If the putt is downhill 8 inches you subtract 8, If its uphill Add 8
Keep it simple, don't make more of it than you have to.
Definitely not trying to make harder than it already is. I was only thinking that if you roll a downhill putt past the hole when you putt back to the cup it will be an uphill putt and the arrow on marker would be pointing up rather than down.
While playing earlier today, I did happen to roll a downhill putt past the hole and saw the arrow pointing up for the putt back to the cup.
Overall... my conclusion is what I first described was a glitch and that can happen. Only other possibility is the cup is on a slope. That I would want to take up with the greens keeper. LOL
Most important, thanks for your feedback. :)