It’s hard to tell without a circuitry layout, but my best guess is that there’s probably capacitors in the power brick acting as an electrical filtration for the motors to make them operate smoothly and reliably.
The capacitors are probably discharging some electricity that are keeping some circuit protective device alive. Unplugging the power brick is probably the only true way to completely remove electricity from the unit.
It’s just a theory based off of my own experience, but if that’s the issue, it kinda depends on how large the capacitors are and what kind of capacity they’re capable of holding.
If it is the issue, I’d expect it to take like 5 minutes for it to discharge completely, but that’s just a guess. If everything is already out of its usual place, you could probably test it if you’re curious enough.