php backtrace bug

phpBacktraceBug.php

<?php

function brokenTrace($arg1, $arg2){
    backtraceWrapper();
    echo exceptionTraceWrapper();
    echo "\n";
    echo "unsetting arg1\n";
    unset($arg1);
    backtraceWrapper();
    echo exceptionTraceWrapper();
    echo "\n";
    echo "unsetting arg2\n";
    unset($arg2);
    backtraceWrapper();
    echo exceptionTraceWrapper();
}

brokenTrace("string", "anything else");
echo "\n";

function backtraceWrapper(){
        $bt = debug_backtrace();
        var_dump($bt[1]['args']);
}

function exceptionTraceWrapper()
{
    $e = new \Exception();
    $trace = explode("\n", $e->getTraceAsString());
    // reverse array to make steps line up chronologically
    $trace = array_reverse($trace);
    array_shift($trace); // remove {main}
    array_pop($trace); // remove call to this method
    $length = count($trace);
    $result = array();

    for ($i = 0; $i < $length; $i++)
    {
        $result[] = ($i + 1)  . ')' . substr($trace[$i], strpos($trace[$i], ' ')); // replace '#someNum' with '$i)', set the right ordering
    }

    return "\t" . implode("\n\t", $result) . "\n";
}