A WebmasterWorld thread reports that Yahoo!'s cache is mishandling the <SUP> </SUP> (superscript) HTML tag. The superscript tag basically looks like this, often used for adding comments1 numbers for reference or other characters to words.
Yahoo! Moderator, jdMorgan, confirmed this as an issue;
In your case it was the </sup> closing tag that got changed to HTML character-entities. In my case, it was the opening <sup> tag. Because of this difference in our applications, it looks like a problem handling <sup>s nested within other tags.
So that's a confirmation of what appears to be a fairly straightforward bug.
Forum discussion at WebmasterWorld.