This problem is not reproducible in YUI 3.
If you are using or even merely hosting any YUI 2 .swf file, please take steps to remove these files immediately from your hosts.
YUI 2 is an end-of-lifed project and is no longer supported. All YUI 2 .swf files have been removed from the Yahoo CDN. If your site was taking advantage of the presence of these files on the Yahoo CDN they will no longer be available.