Google-search – When Google shows single result as two separate ones

Every time you click the star, an AJAX request is sent to the Google servers. Since Google gives no feedback of the request completing, it could be a matter of you refreshing the page too early.

It may be that a certain server/cluster hadn't been updated yet, but the problem should fix itself in a few seconds if that was the case.

Disable it as a user or a webmaster? This is in superuser so assuming its not for a site you control (if it is, use Google Webmaster Tools).

As @MikeKusold pointed out, Greasemonkey is the better option if you use Firefox (or any equivalent for your browser). Looking at the page structure in Firebug, it doesn't seem too hard to write css for a user-defined style to hide them all either; again this would depend on browser support.

Edit: Overlooked that you're using Chrome, don't know if it has a GM equivalent but user style sheets should be an option.