I use a few different Google search queries to track total indexed pages in Google for my site and other sites. These search queries usually give me fairly similar results. The searches are:
1) site:sitename.com inurl:sitename.com
2) site:sitename.com sitename
3) site:sitename.com inurl:sitename
Last night, each of these searches gave me results of about 83,000 indexed pages, give or take a few thousand, for the same site. This morning, I ran the same set of 3 searches. Both #2 and #3 gave me the same ballpark results, but #1 gave me 5,900,000 pages and has remained at that level all day. When I tried to page through some of the 5,900,000 page results on Google, I could not get any further than the first 100 pages. It just stopped. The page structure and layout of the pages of the site in question, have not changed recently, so I don't see this as a possible cause for the odd results. I also seriously doubt the site has 5.9 million pages online.
It looks like a bug, but I was just wondering if anyone has seen anything similar recently or might have any explanation for the results.