You're not nuts._) Without getting into the physics of step motors, look at the problem this way: You store a substantial number of joules in the disk and that stored energy must be removed to decelerate the disc to a stop. There is no mechanism in either the motor or the drive to dissipate this energy, so it is returned (motor acts as generator) back to the power supply. A circuit must be built to dissipate this returned energy, usually as an active clamp across the power supply DC voltage.
Unless I slipped a decimal point, my calculations show 230 Joules (Watt-Sec) of stored energy at 3,000 RPM. That is a substantial amount.
Please see the attached .pdf which goes into a little more detail on this subject.