A normal starter disengages after starting the engine, a dynastarter will have to be engaged all the time I asassume, for the engine to drive it. My stater certainly disengages after start and one time when it didn't due to a fault in the ignition lock, it was over revved, and burned out, and I had to install another old used one.
I believe this is the normal starter for a Volvo MD7a, and I don't see why the engine should be driving a dynastarter and a generator at the same time. But I have no way of telling if somebody exchanged your engines starter with a dynastarter at some point of time. But you can check your self if the starter retracts it gear from the flying wheel after start, and maybe you allready have.
Jesper