JoePublisher - 5:24 pm on May 13, 2011 (gmt 0) [edited by: JoePublisher at 6:17 pm (utc) on May 13, 2011]
@Atomic the code you gave was one of the first things I tried, without 100% success, after going to the iFrame version, deciding I wanted to stick with the XFBML version, and then using the newer SDK asynchronous script as suggested by @DirigoDev the only thing I found which bullet proofed the site 100% (for the last 3 months) was the addition in the .htaccess file which uses a 301 redirect to the 'clean' canonical url just for those visitors (the minority) who trigger the bug - just remember to alter the last line of the code to include your full website home page - either with or without www - i.e. whatever string you use.
either - http://www.example.com
or - http://example.com
Or if you are successful using another method then use what works for you. Just don't leave the problem, it creates duplicate content and really annoys your visitors who trigger the bug - plus any issues that adsense finds.
[edited by: JoePublisher at 6:17 pm (utc) on May 13, 2011]