Thank you very much for trying it out. On mine, both 9 and 10 are set to zero as well. I cannot always reproduce my problem but when it does, it's pretty consistent. It may be scene dependent that camera fails to confuse camera movement and subject movement. With single servo mode, and with [ ] showing, it tries to refocus when I recompose.
I guess Nikon firmware wasn't as advanced as ones it uses today.
Again, thank you very much for trying it out with yours.