I am not sure I have ever experienced what you are talking about. Usually the volume rotation is mechanical, i.e. you have a shaft and a bearing that rotates a mechanical contact breaker so there isn't really any relation between rotation and volume change. And then some volume controls have digital control so the feel is totally decoupled from the electrical system by means of an encoder.
But that doesn't mean you aren't correct. Perhaps the problem is heat related? As your amp heats up, all parts actually increase in size. It's called "thermal expansion" and is the reason you have to have expansion joints in concrete. Maybe after you have had everything on for a while, the shaft is tighter in the bearing and the ball bearings are tighter in the race due to their higher temperature resulting in a "tight" feel. Then when you unplug everything, it all cools and shrinks, yielding a looser volume feel. This definately is happening but I am very impressed you are actually able to notice it. You are anal for sure! haha. Watch me notice it on my premaps from now on thanks to you!
Then again, this is yet another example of what the human brain can do when you truly pay attention to something. It is the very reason we prefer nice stereos to something of lesser quality. Most people would consider us all anal to hear any difference in sound between two components as it is! You are simply all the more sensitive, which is really cool IMO.
Arthur
