Hi,
My customer find … something 
If u wrote in autocomplete field word "constructor" u see in firebug error.
Take a look on http://www.yiiframework.com/doc/api/ and there u can see that problem too.
open firebug and start writing "constructor" (without " "),
after that i get
TypeError: data[0] is undefined
autoFill(q, data[0].value);
jquery...lete.js (wiersz 342)
In my application exist product called "constructor" so in my case is problem.
cheers,
Andrzej