I must endorse helmet fire's comments here - the fact that the AS350 hydraulic jacks can reach a point where they can't overcome the flight loads being placed on them is just something that happens with this particular machine (and others, no doubt) and defines a boundary on the flight envelope.
No matter what type you fly, there will be physical limits to what you can do with it because of the design - for instance, don't try to do a level slow roll in a teetering head helicopter, and whatever other such ridiculous examples you want to name.
I have seen incipient jack stall demonstrated in an AS350, and shown it to others myself as a controlled learning exercise to promote awareness of what can happen if the aircraft is mishandled. This is not a design flaw in the aircraft, it's simply a facet of the machine that people need to be aware of, like VNE or the transmission torque limits; or vortex ring for that matter.
I have flown agressive manoeuvres in the aircraft on many occasions, and have never come anywhere near to jack stall. I would go so far as to say that if you get in a situation where jack stall occurs and you crash because of it, you have caused the crash yourself by placing the aircraft in a situation from which it couldn't recover - something which can be done in any aircraft type!