CodeIgniter:index()开始调用3次?

I've encountered a weird problem. It seems that some of my controllers' index() methods are being executed 3 times when it should only be doing it once. The reason I found this out is because I am logging the number of times the index() method is executed -- and noticed records being inserted in 3s.

At this point, I am at a complete lost. I am unable to describe the problem any further as it is just very odd to me. Any ideas what might be happening?

UPDATE: It seems that the problem only exist when I have JavaScript turned on. When I turned of JavaScript, I no longer get the multiple entries. The problem controllers do have JavaScript. The JS is just some FB plugin and Google AdSense stuff.

I once had this kind of problem, the delay between requests was about 2-5 seconds. The cause was google adsense. It somehow makes another request from it's own server for no reason to the same page. To verify it, just store every requests IP and the user agent, if IP's (user agents too) are different, then you know the cause.

Solution? Give the user some kind of a token before visiting next page - if the token doesn't match on the next request - it's not the same user. Something like a XSRF protection :)