Unfortunately it is becoming more prevalent and open, and the organisers of these rallies are doing less and less about it. If John Key was not of Jewish ancestry, this same malevolent behaviour would still exist, except it would probably only be displayed at anti-Israel rallies. There is a clear commonality between the two, and it is usually just rent-a-crowd attending.
Now what is interesting is that the author of this blog is "Nausea Nissenbaum". I don't know this person, but his/her twitter bio describes themselves as:
"Born on occupied Palestinian land, living on occupied Māori land."They are also heavily active in trying to get BDS to New Zealand (a facebook page of 60 or so likes).
I would ask this person - If you are so proudly "Jewish" that you want to stand up against racism, then what are you doing to identify as such? Can you really just say "I was born a Jew, but I can hate Israel"?
Where is your empathy with Jews living in Israel? Where is the empathy with the constant threat of attack? If it is all "stolen" land, then what about the actual money paid by your ancestors. Or do you think like BDS and you want a Palestine next to a Palestine. Two Islamic states side by side.
Really I am not surprised at all that there is antisemitism at these rallies. What I am surprised about is your naivety about it, and naivety towards the other groups you are involve in.