The "view as" functionality is part of the page cache so you can use this tag to prevent this. I will also have someone investigate why we are cracking open these files if you send me some examples.
How do I keep my page from being cached in Yahoo! Search?
Our search engine contains "snapshots" of the majority of pages discovered during the crawl on the Web and caches them. This enables us to highlight the search terms on text-heavy pages so you can find relevant information quickly. And if the site's server temporarily fails, you can still see the page.
If you run a web site and do not want your content to be accessible through the cache, you can use the NOARCHIVE meta-tag. Place this in the <HEAD> section of your documents:
<META NAME="ROBOTS" CONTENT="NOARCHIVE">
This tag will tell robots not to archive the page. Our crawler will continue to index and follow links from the page, but it will not display a cached page in search results.
Please note that the change will occur the next time the search engine crawls the page containing the NOARCHIVE tag (typically at least once per month).
Also, the NOARCHIVE tag controls only whether the cached page is shown. To prevent the page from being indexed, use the NOINDEX tag. To prevent the crawler from following links, use the NOFOLLOW tag.