Use the sample code below to reproduce the error.  The second parameter of trigger_error does not function, and the error type always shows up as '2'.  I witnessed this running on 4.10 and 4.12.

set_error_handler('ErrorHandler');

function ErrorHandler($number, $description, $file, $line) 
{
    $file = preg_replace('/\\\\/','/',$file);
    $message = $description . " at line " . $line . " in ". 
        $file . " and error type ".$number;
    print "<script language='JavaScript'>alert('$message')</script>";
    exit -1;
}

trigger_error("Testing",E_ERROR);