Description:
------------
If a variable is set to a string and isset() is used to check an array key for that variable it returns true.

Reproduce code:
---------------
$var="foo";
if(isset($var['ed']))
{
        //why are we in this section if $var is a string?
	if(is_array($var))
	{
                // This doesn't happen
		echo "It's an array";
	}
	else
	{
                // And yet this returns "f"
		echo $var['ed'];
	}
}


Expected result:
----------------
I would expect isset to return false;

Actual result:
--------------
isset returns true, because a check for any associative array index for the var will return the first character.