I agree that it IS good airmanship to cover the thrust levers when (a) they are being moved by the autothrottle system, and (b) below MSA and close to the ground. The same goes for the flying controls.
I once selected climb thrust in the 737 (CL) and the thrust levers closed at 1500 feet! Since then I will always cover them after take-off!
Also LEM , if you are not happy with the habits of your co-pilots and you feel that what they are doing is the wrong thing then don't come on here making yourself look like a classic "P minus, G Plus" Captain, just discretely discuss it with your training department.