What do you mean?

ASX300 rebalance will be effective before opening on Monday 20/9, so the standard practice is any index funds following ASX300 will dump any stock that will be excluded (in this case HUM) at the last closing auction (i.e. today) to follow as closely as the ASX300 index itself.
What I was saying, was that shorts could be jumping in after announcement of rebalance to sell first but buy back when index funds finally sell their holdings, which effectively prevents a sudden price drop but spread the pain of declining sp over a few days. Was just noticing this could be the case here and wondering if this little arbitrage exercise is the norm these days..

What do you mean?