I was not able to reproduce the problem. Here is your script modified to show a little more info:

 Code:
? @kix
$a="1","","2","3","","5","6","7","8","9","10",19,"9"
? "Return All Exact Matches:" + Join( AScan($a,"9",,,2) , ",") 
? "Return All Instr Matches:" + Join( AScan($a,"9",,,3) , ",")


4.64 returns
 Code:
4.64
Return All Exact Matches:9,12
Return All Instr Matches:9,11,12


4.62 returns the same