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This is a little surprising. If the index.html was optimized for another engine, or if there is a meta refresh, then this could be a problem.
Has this always been an AV pattern? I will watch my rankings and see if it causes a drop. This index.html spidering trend throughs another wrench into SEO efforts, because no matter how well you make a page -- it is very difficult for it to match each search engine's algorithum.
Many people submit only their home page or a hallway page and wait for the spider to find the rest of the pages on his own - "found" pages sometimes rank better than submitted pages. (This approach takes a lot of patience.)
If you have pages you don't want a particular SE to see, you should exclude them in your robots.txt file.