According to Fatsoh it's the ASX who makes the call. I wonder what criteria they use for such decisons since the share has been pretty lonely for some time now and all of a sudden volume is in excess of 3mill and price up 12%.
( http://www.hotcopper.com.au/post_single.asp?fid=4&tid=565754&sym=&MSGNO=368678#368678 )