The blades on an RC helicopter are able to lead and lag (due to them being attached to the rotor head by just one bolt on each blade). The rotor head is then attached to the mast in such a way that the blades can effectively sea-saw up and down (flap). However, there is then a very stiff rubber damper which opposes this sea sawing movement. In these aerobatic helicopters, the rubber is particularly stiff. In effect, mast bumping is happening all of the time, but the shock of impact is absorbed by these rubber dampers. This system causes the body of the helicopter to follow the plane of the rotor disk very very rapidly, and so when pitching up, the blades never impact the tail, because it is pitching as rapidly as the rotor disk.
Also, there is hardly any coning angle, due to the very low disk loading compared to a full sized helicopter.