In the Beech community, it is speculated that the throttle friction locks were not set properly. On the KingAir, the throttle is spring loaded to return to idle if released, unless the friction lock is set tight enough. If the throttle is not full open, but slightly retarded, the auto-feather function is disabled.
Taking your hand off the throttle for raising the gear may cause the throttle to slip, if you have an engine failure at that time, with no auto-feather available, not many options are left.