While I don't think Bernie should have been interrupted, that is what demonstrators are supposed to do as far as trying to get as much attention as possible. Was it a bad move? Sure. Was it effective? Very much so. Had they tried at another place it might not have made news at all considering they would have got moved right away.
And the reason this doesn't happen at a Hilary event is because she has a legit security detail, she is Hilary Clinton. Bernie is a senator from a tiny state, she as been at the top levels of our government. I support Bernie 1000% over Hilary but don't be fooled. You are talking about a professional, seasoned and well financed campaign vs a guy with great ideas.
The fact this keeps happening to him does reek of someone getting greased to do it. I just hope this wasn't one of those times.