I think this is a simply "wasteful" bug rather than actually causing an application failure of any kind.

Problem

libraries/joomla/application/route.php, line 58.
_
if (!is_array($url) && (strpos($url, '&') !== 0) && (strpos($url, 'index.php') !== 0))_

the latter two checks fail if either item checked for is at the beginning of the string checked.

This is perhaps unlikely for "&", but almost guaranteed for "index.php".

The router is always re-executed because of this,even if it's not required.

Solution

Change the line to

if (!is_array($url) && !(strpos($url, '&') === false) && !(strpos($url, 'index.php') === false))

How many other places in the codebase are like this?