Is it a bug in Chrome or Facebook's Fan Box? I am not sure about but looks like a bug in Google chrome.
I tested the Fan box on Mozilla and Internet explorer and they both show the same Fans count but chrome somehow makes me feel happier as it always shows the count with an added fan.
Initially I thought that it might be an issue with the Facebook fan code that i have used on my blog. I quickly verified it on one of the most famous blogs and found the same results.
Check yours and you may also be surprised by Chrome!! And yes, it is not the case where a new fan has been added while switching between browsers. I have tried it multiple times in a day and the results were same.
Today, i was again looking into this issue and found that if you are logged into your Facebook account, then the fans count increase by one (1) in all browsers and decrease by 1 if otherwise. I am not sure why is this happening though.