The only thing readily apparent is some users have to be told that they are overvolting the CPU. Since all VID Special Add voltages are in red to indicate overvoltage this setting would need to be locked out below the default voltage for the red indication to be true.

Selecting any voltage between Auto and what the board considers default in VID Control results in VID Special Add being locked out. This would indicate there isn't a specific issue with Auto itself and VID Special Add being used together. I can only think of a couple of reasons besides the one above why this has been done.

The advantage of using Auto in VID Control in combination with VID Special Add was overlooked.

There is an issue when using VID Special Add with any voltage below default. Of the boards I have here, both P35 and X38, I have seen no issue with this combination. The voltages have been monitored using a 350MHz scope with glitch capture which would show any voltage spike.

Will try to get clarification on this. Being the weekend it might be a day or so though.