Maybe the difference is related to:

http://forum.avast.com/index.php?topic=84334.msg686091#msg686091 :

There is currently a dependency between Script and Behavior Shields

and maybe that’s why Vlk was so interested in DBone’s explanation:

http://forum.avast.com/index.php?topic=84297.msg686431#msg686431.

Of course, I am just guessing.