I think its a hidden Windows feature/bug/annoyance. My br writer does the same thing when I plug in anything. Its also after I clean install gfx drivers which means removing the old. I think what you said is right, its like a driver search. It does not display this behavior in Linux.
I don't really notice the other HDD turning off if it does, but I have my system power settings set to maximum possible settings at all times. It never sleeps, it doesn't hibernate, and any configurable option that has a suggestion that it may want to reduce power to some component I have turned off. Not even LAN card is allowed to taper down in any instance. I don't think its turns off on my system really. I always have access to it and never heard it stop spinning before.
Maybe there's a power setting allowing it to turn off?
My laptop makes your desktop self-conscious~ Now with more Hello Kitty!:o