If you lower the lever in pretty much any helicopter, the disc will flap forward and the nose will drop - if you then haul back on the cyclic you are going to have the disc coming back while the tail is still going up. If your control margins are reduced (C of G) and your control power is low (type of rotor head) it is not a surprise that the rotors might meet the tail.
Perhaps the 600 is more susceptible than other helos, hence the RFM text but high speed cruise entry to auto does require more careful handling and those pilots used to 'standard' 90 knot entries may well be surprised at the aircraft response to their normal control inputs.