Andy675,
There is no doubt that the behaviour shield does something, even if that "something" so far appears to have only been identified as some of the various problems it seems to cause, like one I posted about it preventing me printing from secure pages to my PDF printer in IE7, but not in Firefox. That post received no responses.
There are a lot of posts with queries as to what the behaviour shield is supposed to do, whether it blocks or doesn't block, what is its relationship to the community setting - some users have made guesses, but significantly there seems to have been no definitive comment by Avast.
I even sent an email to VLK some days ago, asking him whether he could clear up some of the confusion, but that too so far remains unanswered.