Are you turning when passing through this speed range?
If my rapidly failing memory is right, below 60-65 knots the yaw channel is trying to maintain heading, and above 60-65 knots it's trying to maintain balanced flight.
Can't remember what the sensor is that tells the AFCS that the pilot is trying to over-ride the yaw channel, but that might also be a problem.
Does it do it on all 412s or just one?