Was looking through the changelog for v1.6 and realized you had addressed a bug I had been seeing on a recent project regarding Firefox and Chrome caching the URLStream used to audit the size of a load. However, your fix in LoaderItem.as isn't correct. Applying the cacheBusterID to the LoaderItem's URLRequest will still give the audit stream and load proper the same url, so the stream could still get cached. Here's a screenshot of the post-v1.6 behavior in action as seen through Charles:
As you can see, the helvetica-neue.swf loads twice, once for the audit, once for the load, but the second load is half the size. This swf is 80K+. Notice that the cacheBusterID for each request is the same, this is the issue.
My fix has been to remove the cacheBusterID assignment from LoaderItem.auditSize and to make the URLStream use a different URLRequest with an explicitly different query string parameter than the actual request to ensure we will always avoid caching the audit.
/*_applyCacheBuster(); //to work around bugs in Chrome and Firefox that can cause them to use the partially-loaded audit file in the cache instead of loading the full file normally.*/
_auditStream.load( new URLRequest( _url + ((_url.indexOf("?") == -1) ? "?" : "&") + 'purpose=audit' ) );
Hope this helps, and thanks for all your work.