It looks like URL of that article is case-insensitive and page does not specify canonical URL. Both: http://www.isolani.co.uk/blog/javascript/BreakingTheWebWi

It looks like URL of that article is case-insensitive and page does not specify canonical URL. Both: http://www.isolani.co.uk/blog/javascript/BreakingTheWebWithHashBangs http://www.isolani.co.uk/blog/javascript/BreakingTheWebWithH... and: http://www.isolani.co.uk/blog/javascript/breakingthewebwithhashbangs http://www.isolani.co.uk/blog/javascript/breakingthewebwithh... render the same content, and <link rel="canonical"> does not exist in source code of that page.