This question already has an answer here:
Google has processed my XML sitemaps, and for one of the files, Webmaster Tools claims to have indexed 44,797 links even though that file only contains 4,582 links.
Here's a screen cap:
I'm not terribly worried about this, but it is a curious state of affairs, and I'm sure there's something to be learned from it. What's going on?
UPDATE: This is not a duplicate of the question: "Why is there a difference between urls submitted to a sitemap and urls in the google index?" Here's why, as I explained in the comment below:
I understand that Google may index many pages that are not in my sitemap. In fact, Webmaster Tools indicates that there are many thousands of such pages. What's curious here is that the above table is supposed to report how many of the links in a particular sitemap file have been selected for the index, so it would seem to be impossible for this number to exceed the number of links actually in the file. Unless, of course, I'm missing something.
One theory: Could it be possible that many versions of the same pages -- perhaps with different params -- have been indexed?