See my Post 140 on page 7...
Already 2 days ago I discreetly mentioned this scenario. Personally, I agree with Belgique as this seems at the moment a plausable and realistic scenario.
For those not familiar with the B737:
On a Dual-Autopilot approach, the aircraft back-trims at around 400'. In case of a subsequent manual GA (normally the autopilot handles the GA) for whatever reason, a downward force is needed on the joke to avoid over-rotation...this can surprise sometimes new left-seaters during their sim-training.