Strange Indexed Pages Quantity

Recently I have noticed that quantity of my “indexed pages” in Google has overcome real quantity of pages on my site. The real quantity is 150 pages, while Google shows bout 300. Checking and counting indexed pages through “site:” search, I found actual quantity of indexed pages and number of pages displayed by Google differ. It is more likely to be a bug, but I think that it can be some kind of concealment, just like they’ve did it with backward links.