tempnam() not working as expected...

Can someone explain the following to me: <?php $d=tempnam(".","dir"); /* create a temp named file */ unlink($d); /* unlink it because we're going to make it a directory */ mkdir($d,777,true); /* make the directory */ echo "$d is ". (is_dir($d)?'':'NOT')." a directory\n"; $f=tempnam($d,"file"); /* using the first directory, create a new temp named file */ unlink($f); /* unlink it as we're going to make it a directory */ mkdir($f,777,true); /* make the directory */ echo "$f is ". (is_dir($f)?'':'NOT')." a directory\n"; ?> /Users/tamara/Sites/gallery/lib/common/t/dirGuWOLW is a directory /private/var/folders/pI/pIx-p0mhH5eEQ64yAiDQmE+++TI/-Tmp-/fileC7Rnzg is a directory Why isn't the second tempnam using the directory path I pass to it? The strange thing I notice is that if I pass in a directory path to tempnam that was NOT created initially by tempnam, it works: miishka:t tamara$ mkdir a miishka:t tamara$ php -r 'echo tempnam("/Users/tamara/Sites/gallery/lib/common/t/a","file").PHP_EOL;' /Users/tamara/Sites/gallery/lib/common/t/a/filepSwRzF miishka:t tamara$