This is not a bug, but rather a small request.

I like the topsites setting, but I would like it to be ready to overwrite as default.

Now you have to klick on the address bar twice to mark "topsites://" and then over write it with a web address. I would like it that when you open a new tab and get the topsites, you can start writing a new address on your keyboard without having to klick on the address bar first.