I set a breakpoint in libs\Application.php in __construct() and found it was getting hit twice.
The second hit is a get of favicon.ico and it was not found so it looks like there is a behind-the-scenes redirect to the error page happening. However, there is no visual effect on the rendered page view.
This seems like extra and unnecessary work going on.
What I did was under this line:
if ($this->url_controller) {
I added this:
if ($this->url_controller == 'favicon.ico') {
return;
}
I don't know if that's the best way but it seems to be working for me.