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Make that redirect work for the root and for all folders, stripping the index filename off for all (and preserving the rest of the path).
Details and code can be found in the WebmasterWorld Apache forum.
It seems that the server sometimes (when Google visits) redirects "/" to "index.html".
That's something to track down and fix - most esepcially if search engine bots are being treated differently than the regular browsers. The domain root (or directory root) should resolve directly with no redirects needed.
Here's a thread that discusses the domain root versus index.html issue in more detail: