Missed this thread due to holidays. As AWBD says, the problem arises from the large amount of tailrotor thrust that can be generated by right pedal. The couple between the high tailrotor and the wheels can be enough to cause rollover. Taxy speed has nothing to do with it- you can make it roll over when its stationary if you try hard enough, esp. with a crosswind, deck motion etc
Lateral cyclic can be used to make the articulated head generate a couple in the opposite direction to cancel out (or at least reduce) the rollover couple - ie move cyclic and pedals in the same direction. One problem can occur is that there is no indication for dumb pilots as to what is the neutral position for the cyclic - thus its possible for someone to have right pedal and left cyclic without realising it. Not a good situation!
As others said, best to limit right pedal - use differential braking and avoid tight right turns, esp when light (vertical centre of gravity rises when there is not much fuel and no pax - high centre of gravity = more likely to roll over).
Interestingly on the EC225 they have changed the "gearing" between collective and pedals so that with the lever down, full right pedal gives less thrust than on the 332 and 330. For taxying straight ahead, pedal position is about 30% to the right from centre, but as you raise the lever it becomes more in the middle so pedal authority in the hover in undiminished (in fact more thrust due to increase weight / power). The undesireable side effect of this is that when you do a running landing, you have to feed in a lot of right pedal as you lower the lever after touchdown, otherwise it hurtles off to the left!
HC