It can also be partly the engineers faux pas if he spins the drivers or opens or closes the throttle too quickly when switching without the fireman being prepared on an oil burner. Then you have to ask why wasn't the fireman prepared? Maybe the fireman's attention was on starting the injector, or adjusting the fire, or watching for signals, which are all legitimate tasks or maybe the fireman was inattentive. The cab crew usually try to cooperate to avoid these kind of things like the engineer calling out "gonna open up" or "dropping down a notch" and so on.