I'm not an expert in these things by any means! However, my understanding is that if a substantial holders holdings move by more than a certain percentage the market should be advised accordingly.
I have had a quick look around on the internet to see if I can determine what that percentage is.
It appears that the submission of substantial holder notices is regulated under section 671B of the Corporations Act 2001.
In the link below it indicates advice has to be given for movements of 1% of their holdings.