The above comment explains it, sorry I was logged into the wrong account when I made it. Regardless, I’m not sure this is an “issue” per se, since it doesn’t affect anyone’s ability to use grabicon.

Google’s favicon service is “free” in the same way that your neighbor’s unsecured WiFi is “free”. It was never intended to be used by others, but it was never locked down, either. That’s why you can’t find documentation from Google itself. While it does currently work, it only provides 16px icons, and could go away at any time.

See this article for more info:

http://www.rubycuts.com/2015/01/ditch-googles-blase-favicon-service-grabicon-loves-you/