My money's on 9. I have some yarn on a circ needle to try some st that people ask about. I can explain it better if I do it. This pattern knits 9 and decreases at the end, purl 9 decrease at end, k9 dec at end, p9 dec at end. I don't know what this instep is supposed to look like, but when you work the st like that it seems to be even on both sides and is definitely some kind of shaping.
Yeah, its 9. I just messed around with it again and you're basically working the center 9 st in st st and when you dec at the end you're taking one st from the st on the sides of the 9. If you do it, you'll see.
If you do it and it's wrong, just send it to me and I'll frog it for you.